Rapid Climate Change Is Not Unique to the Present

Rapid climate change, such as the accelerated warming of the past 40 years, is not a new phenomenon. During the last ice age, which spanned the period from about 115,000 to 11,000 years ago, temperatures in Greenland rose abruptly and fell again at least 25 times. Corresponding temperature swings occurred in Antarctica too, although they were less pronounced than those in Greenland.

The striking but fleeting bursts of heat are known as Dansgaard–Oeschger (D-O) events, named after palaeoclimatologists Willi Dansgaard and Hans Oeschger who examined ice cores obtained by deep drilling the Greenland ice sheet. What they found was a series of rapid climate fluctuations, when the icebound earth suddenly warmed to near-interglacial conditions over just a few decades, only to gradually cool back down to frigid ice-age temperatures.

Ice-core data from Greenland and Antarctica are depicted in the figure below; two sets of measurements, recorded at different locations, are shown for each. The isotopic ratios of ¹⁸O to ¹⁶O, or δ¹⁸O, and ²H to ¹H, or δ²H, in the cores are used as proxies for the past surface temperature in Greenland and Antarctica, respectively.

Multiple D-O events can be seen in the four sets of data, stronger in Greenland than Antarctica. The periodicity of successive events averages 1,470 years, which has led to the suggestion of a 1,500-year cycle of climate change associated with the sun.

Somewhat similar cyclicity has been observed during the present interglacial period or Holocene, with eight sudden temperature drops and recoveries, mirroring D-O temperature spurts, as illustrated by the thick black line in the next figure. Note that the horizontal timescale runs forward, compared to backward in the previous (and following) figure.

These so-called Bond events were identified by geologist Gerard Bond and his colleagues, who used drift ice measured in deep-sea sediment cores, and δ¹⁸O as a temperature proxy, to study ancient climate change. The deep-sea cores contain glacial debris rafted into the oceans by icebergs, and then dropped onto the sea floor as the icebergs melted. The volume of glacial debris was largest, and it was carried farthest out to sea, when temperatures were lowest.

Another set of distinctive, abrupt events during the latter part of the last ice age were Heinrich events, which are related to both D-O events and Bond cycles. Five of the six or more Heinrich events are shown in the following figure, where the red line represents Greenland ice-core δ¹⁸O data, and some of the many D-O events are marked; the figure also includes Antarctic δ¹⁸O data, together with ice-age CO₂ and CH₄ levels.

As you can see, Heinrich events represent the cooling portion of certain D-O events. Although the origins of both are debated, they are thought likely to be associated with an increase in icebergs discharged from the massive Laurentide ice sheet which covered most of Canada and the northern U.S. Just as with Bond events, Heinrich and D-O events left a signature on the ocean floor, in this case in the form of large rocks eroded by glaciers and dropped by melting icebergs.

The melting icebergs would have also disgorged enormous quantities of freshwater into the Labrador Sea. One hypothesis is that this vast influx of freshwater disrupted the deep-ocean thermohaline circulation (shown below) by lowering ocean salinity, which in turn suppressed deepwater formation and reduced the thermohaline circulation.

Since the thermohaline circulation plays an important role in transporting heat northward, a slowdown would have caused the North Atlantic to cool, leading to a Heinrich event. Later, as the supply of freshwater decreased, ocean salinity and deepwater formation would have increased again, resulting in the rapid warming of a D-O event.

However, this is but one of several possible explanations. The proposed freshwater increase and reduced deepwater formation during D-O events could have resulted from changes in wind and rainfall patterns in the Northern Hemisphere, or the expansion of Arctic sea ice, rather than melting icebergs.

In 2021, an international team of climate researchers concluded that when certain parts of the ice-age climate system changed abruptly, other parts of the system followed like a series of dominoes toppling in succession. But to their surprise, neither the rate of change nor the order of the processes were the same from one event to the other.

Using data from two Greenland ice cores, the researchers discovered that changes in ocean currents, sea ice and wind patterns were so closely intertwined that they likely triggered and reinforced each other in bringing about the abrupt climate changes of D-O and Heinrich events.

While there’s clearly no connection between ice-age D-O events and today’s accelerated warming, this research and the very existence of such events show that the underlying causes of rapid climate change can be elusive.

Next: Challenges to the CO2 Global Warming Hypothesis: (11) Global Warming Is Driven by Oceanic Seismic Activity, Not CO2

Hottest in 125,000 Years? Dishonest Claim Contradicts the Evidence

Amidst the hysterical hype in the mainstream media about recent heat waves all over the Northern Hemisphere, especially in the U.S., the Mediterranean and Asia, one claim stands out as utterly ridiculous – which is that temperatures were the highest the world has seen in 125,000 years, since the interglacial period between the last two ice ages.

But the claim, repeated mindlessly by newspapers, magazines and TV networks in lockstep, is blatantly wrong. Aside from the media confusing the temperature of the hotter ground with that of the air above, there is ample evidence that the earth’s climate has been as warm or warmer than today’s – and comparable to that 125,000 years ago – several times during the past 11,000 years after the last ice age ended.

Underlying the preposterous claim is an erroneous temperature graph featured in the 2021 Sixth Assessment Report of the IPCC (Intergovernmental Panel on Climate Change). The report revives the infamous “hockey stick” – a reconstructed temperature graph for the past 2020 years resembling the shaft and blade of a hockey stick on its side, with no change or a slight decline in temperature for the first 1900 years, followed by a sudden, rapid upturn during the most recent 120 years.

Prominently displayed near the beginning of the report, the IPCC’s latest version of the hockey stick is shown in the figure above. The solid grey line from 1 to 2000 is a reconstruction of global surface temperature from paleoclimate archives, while the solid black line from 1850 to 2020 represents direct observations. Both are relative to the 1850–1900 mean and averaged by decade.

But what is missing from the spurious hockey stick are two previously well-documented features of our past climate: the MWP (Medieval Warm Period) around the year 1000, a time when warmer than normal conditions were reported in many parts of the world, and the cool period centered around 1650 known as the LIA (Little Ice Age).

The two features are clearly visible in a different reconstruction of past temperatures by Fredrik Ljungqvist, who is a professor of geography at Stockholm University in Sweden. Ljungqvist’s 2010 reconstruction, for extra-tropical latitudes (30–90°N) in the Northern Hemisphere only, is depicted in the next figure; temperatures are averaged by decade. Not only do the MWP and LIA stand out, but the end of the Roman Warm Period at the beginning of the previous millennium can also be seen on the left.

Both this reconstruction and the IPCC’s are based on paleoclimate proxies such as tree rings, marine sediments, ice cores, boreholes and leaf fossils. Although other reconstructions have supported the IPCC position that the MWP and LIA did not exist, a large number also provide strong evidence that they were real.

A 2016 summary paper by Ljungqvist and a co-author found that of the 16 large-scale reconstructions they studied, 7 had their warmest year during the MWP and 9 in the 20th century. The overall choice of research papers that the IPCC’s report drew from is strongly biased toward the lack of both the MWP and LIA, and many of the temperature reconstructions cited in the report are faulty because they rely on cherry-picked or incomplete proxy data.

A Southern Hemisphere example is shown in the figure below, depicting reconstructed temperatures for the continent of Antarctica back to the year 500. This also reveals a distinct LIA and what appears to be an extended MWP at the South Pole.

The hockey stick, the creation of climate scientist and IPCC author Michael Mann, first appeared in the IPCC’s Third Assessment Report in 2001, but was conspicuously absent from the fourth and fifth reports. It disappeared after its 2003 debunking by mining analyst Stephen McIntyre and economist Ross McKitrick, who found that the graph was based on faulty statistical analysis, as well as preferential data selection (see here and here). The hockey stick was also discredited by a team of scientists and statisticians assembled by the U.S. National Academy of Sciences.

Plenty of evidence, including that presented here, shows that global temperatures were not relatively constant for centuries as the hockey stick would have one believe. Maximum temperatures were actually higher than now during the MWP, when Scandinavian Vikings farmed in Greenland and wine was grown in the UK, and then much lower during the LIA, when frost fairs on the UK’s frozen Thames River became a common sight.

In a previous post, I presented evidence for a period even warmer than the MWP immediately following the last ice age, a period known as the Holocene Thermal Maximum.

Next: Record Heat May Be from Natural Sources: El Niño and Water Vapor from 2022 Tonga Eruption

Challenges to the CO2 Global Warming Hypothesis: (8) The Antarctic Centennial Oscillation as the Source of Global Warming

Possibly overlooked at the time it was published, a 2018 paper on Antarctica presents an unusual challenge to the CO₂ global warming hypothesis, which postulates that observed global warming – currently about 0.9 degrees Celsius (1.6 degrees Fahrenheit) since the preindustrial era – has been caused primarily by human emissions of CO₂ and other greenhouse gases into the atmosphere.

The proposed challenge is that current global warming can be explained by a natural ocean cycle known as the ACO (Antarctic Centennial Oscillation), the evolutionary precursor of today’s AAO (Antarctic Oscillation), also called the SAM (Southern Annular Mode). This unconventional idea comes from a group of researchers at the Environmental Studies Institute in Santa Cruz, California.

The Santa Cruz group points out that global temperatures have oscillated for at least the last 542 million years, since the beginning of the current Phanerozoic Eon. Superimposed on multi-millennial climate cycles are numerous shorter global and regional cycles ranging in period from millennia down to a few weeks. Among these are numerous present-day ocean cycles, including the above AAO, ENSO (the El Niño – Southern Oscillation) and the AMO (Atlantic Multidecadal Oscillation).

In their 2018 paper the researchers report on the previously unexplored ACO, the record of which is entrained in stable isotopes frozen in ice cores at Vostok in Antarctica and three additional Antarctic drill sites widely distributed on the East Antarctic Plateau, namely, EPICA (European Project for Ice Coring in Antarctica) Dronning Maud Land, EPICA Dome C and Talos Dome.

Past surface temperatures were calculated from the ice cores by measuring either the oxygen ¹⁸O to ¹⁶O, or hydrogen ²H to ¹H, isotopic ratios. Precise ice-core chronology enabled the paleoclimate records from the four drill sites to be synchronized in time.

In analyzing the ice-core data, the paper’s authors found a prominent cycle with a mean repetition period of 352 years over the time interval they evaluated, from 226,400 years before 1950 to the year 1801. Identified as the ACO, the cycle time series nevertheless shows a progressive increase in both frequency and amplitude or temperature swing, the period shortening as the amplitude increases proportionally.

The figure below illustrates the cycle’s temperature oscillations, as measured at Vostok for the last 20,000 years. LGM is the Last Glacial Maximum, LGT the subsequent Last Glacial Termination, and the time scale is measured in thousands of years before 1950 (Kyb1950). The top panel shows temperatures from the LGM to the present, while the lower four panels show the record on an expanded time and temperature scale, with every identified ACO cycle labeled. The small blue and red numbers designate smaller-amplitude oscillations (approximately 10% of all cycles identified), which were found at all four drill sites.

The steady decline of the ACO period over 226 millennia, and the corresponding rise in temperature swing, are depicted in the next figure for the Vostok record. Here individual records have been averaged over 5,000-year intervals. Without averaging, the period ranges from 63 to 1,174 years, and the cycle temperature swing varies from 0.05 degrees Celsius (0.09 degrees Fahrenheit) to as much as 3.2 degrees Celsius (5.8 degrees Fahrenheit).

Because of the variation in period (frequency) and amplitude, the null hypothesis that the observed cycles represent random fluctuations in cycle structure was tested by the researchers, using the statistical concept of autocorrelation. This confirmed that the cycle structure was indeed nonrandom. However, the data for the whole 226,400 years did reveal evidence for other, lower-frequency cycles, including ones with periods of 1,096 and 1,470 years.

So how is all this connected to global warming?

The variable ACO cycles show that temperature fluctuations of several degrees Celsius have occurred many times in the past 226 millennia, including our present Holocene (c and d in the first figure above) – at least in Antarctica. That these Antarctic cycles extend globally was inferred by the researchers from the correspondence between the 1,096- and 1,470-year ACO cycles mentioned above and so-called Bond events in the Northern Hemisphere, which are thought to have the same periodicity but occur up to 3 millennia later.

Bond events refer to glacial debris rafted into the North Atlantic Ocean by icebergs and then dropped onto the sea floor as the icebergs melt.  The volume of glacial debris, which is measured in deep-sea sediment cores, fluctuates as global temperatures rise and fall.

1,096 and 1,470 years are also approximate multiples of the mean ACO period of 352 years. This finding, together with the observation about Bond events, is considered by the researchers to be strong evidence that the ACO is a natural climate cycle that arises in Antarctica and then propagates northward, influencing global temperatures. It’s feasible that our current global warming – during which temperatures have already risen by close to 1 degree Celsius (1.8 degrees Fahrenheit) – is simply part of the latest ACO (or AAO/SAM) cycle.

Such speculation, however, needs to be reinforced by solid scientific evidence before it can be considered a serious challenge to the CO₂ hypothesis.

Next: No Evidence That Extreme Weather on the Rise: A Look at the Past - (1) Hurricanes

Climate Heresy: To Avoid Extinction We Need More, Not Less CO2

A recent preprint advances the heretical idea that all life on Earth will perish in as little as 42,000 years unless we take action to boost – not lower – the CO₂ level in the atmosphere. The preprint’s author claims that is when the level could fall to a critical 150 ppm (parts per million), below which plants die due to CO₂ starvation.

Some of the arguments of author Brendan Godwin, a former Australian meteorologist, are sound. But Godwin seriously underestimates the time frame for possible extinction. It can easily be shown that the interval is in fact millions of years.

Plants are essential for life because they are the source, either directly or indirectly, of all the food that living creatures eat. Both CO₂ and water, as well as sunlight, are necessary for the photosynthesis process by which plants grow. In the carbon cycle, the ultimate repository for CO₂ pulled out of both the air and the oceans is limestone or calcium carbonate (CaCO₃), of which there are two types: chemical and biological.

Chemical limestone is formed from the weathering over time of silicate rocks, which make up about 90% of the earth’s crust, and to a lesser extent, of carbonate rocks. Silicate weathering draws CO₂ out of the atmosphere when the CO₂ combines with rainwater to form carbonic acid (H₂CO₃) that dissolves silicates. A representative chemical reaction for calcium silicate (CaSiO₃) is

CaSiO₃ + 2CO₂ + H₂O → Ca²⁺ + 2HCO₃^- + SiO₂.

The resulting calcium (Ca²⁺) and bicarbonate (HCO₃^-) ions, together with dissolved silica (SiO₂), are then carried away mostly by rivers to the oceans. There, calcium carbonate (CaCO₃) precipitates when marine organisms utilize the Ca²⁺ and HCO₃^- ions to build their skeletons and shells:

Ca²⁺ + 2HCO₃^- → CaCO₃ + CO₂ + H₂O.

Once the organisms die, the CaCO₃ skeletons and shells sink to the ocean floor and are deposited as chemical limestone in deep-sea sediment.

Biological limestone, on the other hand, comes from fossilized coral reefs and is approximately twice as abundant as chemical limestone. Just like the marine organisms or plankton that ultimately form chemical limestone, the polyps that constitute a coral build the chambers in which they live out of CaCO₃. Biological limestone from accumulated coralline debris accumulates mainly in shallow ocean waters, and is transformed over time by plate tectonic processes into major outcrops on land and in the highest mountains – even the top of Mount Everest.

Godwin’s estimate of only 42,000 years before life is extinct stems from a misunderstanding about the carbon cycle, which is illustrated in the figure below depicting the global carbon budget in gigatonnes of carbon. Carbon stocks are shown in blue, with annual flows between carbon reservoirs shown in red.

The carbon sequestered as chemical limestone in deep-sea sediment, and as biological limestone, is represented by the 100 million gigatonnes stored in the earth’s crust. As you can see, today’s atmosphere contains approximately 850 gigatonnes of carbon (as CO₂) and the oceans another 38,000 gigatonnes, most of which was originally dissolved as atmospheric CO₂.

The erroneous estimate of Godwin simply divides the 38,000 gigatonnes of carbon in the oceans by 0.9 gigatonnes per year, which is the known rate of carbon sequestration into chemical and biological limestone combined; chemical weathering of silicate rocks contributes 0.3 gigatonnes per year, while fossilized coral contributes 0.6 gigatonnes per year.

This calculation is wrong because Godwin fails to understand that the carbon cycle is dynamic, with carbon constantly being exchanged between land, atmospheric and ocean reservoirs. The carbon sequestered into chemical and biological limestone is included in the flow from rivers to ocean and in ocean uptake in the figure above. But there are many flows in the opposite direction that replenish carbon in the atmosphere, even when fossil fuel burning is ignored. Simply depleting the ocean reservoir will not lead to extinction.

A realistic estimate can be made by assuming that atmospheric carbon will continue to decline at the same rate as it has over the past 540 million years. As shown in the next figure, the concentration of CO₂ in the atmosphere over that period has dropped from a high of about 7,000 ppm at the beginning of the so-called Cambrian Explosion, to today’s 417 ppm.

Using a conversion factor of 2.13 gigatonnes of carbon per ppm of atmospheric CO₂, the drop corresponds to an average decline of approximately 26 kilotonnes of carbon per year. At that rate, the 150 ppm (320 gigatonnes) level at which life on earth would begin to die will not be reached until 22 million years from now.

Given that the present CO₂ level is rising due to fossil fuel emissions, the 22 million years is likely to be an underestimate. However, ecologist Patrick Moore points out that a future cessation of fossil fuel burning could make the next ice age – which may be only thousands of years away – devastating for humanity, as temperatures and CO₂ levels could fall to unprecedentedly low levels, drastically reducing plant growth and creating widespread famine.

Next: New Research Finds Climate Models Unable to Reproduce Ocean Surface Temperatures

Challenges to the CO2 Global Warming Hypothesis: (7) Ocean Currents More Important than the Greenhouse Effect

A rather different challenge to the CO₂ global warming hypothesis from the challenges discussed in my previous posts postulates that human emissions of CO₂ into the atmosphere have only a minimal impact on the earth’s temperature. Instead, it is proposed that current global warming comes from a slowdown in ocean currents.

The daring challenge has been made in a recent paper by retired Australian meteorologist William Kininmonth, who was head of his country’s National Climate Centre from 1986 to 1998. Kininmonth rejects the claim of the IPCC (Intergovernmental Panel on Climate Change) that greenhouse gases have caused the bulk of modern global warming. The IPCC's claim is based on the hypothesis that the intensity of cooling longwave radiation to space has been considerably reduced by the increased atmospheric concentration of gases such as CO₂.

But, he says, the IPCC glosses over the fact that the earth is spherical, so what happens near the equator is very different from what happens at the poles. Most absorption of incoming shortwave solar radiation occurs over the tropics, where the incident radiation is nearly perpendicular to the surface. Yet the emission of outgoing longwave radiation takes place mostly at higher latitudes. Nowhere is there local radiation balance.

In an effort by the climate system to achieve balance, atmospheric winds and ocean currents constantly transport heat from the tropics toward the poles. Kininmonth argues, however, that radiation balance can’t exist globally, simply because the earth’s average surface temperature is not constant, with an annual range exceeding 2.5 degrees Celsius (4.5 degrees Fahrenheit). This shows that the global emission of longwave radiation to space varies seasonally, so radiation to space can’t define Earth’s temperature, either locally or globally.

In warm tropical oceans, the temperature is governed by absorption of solar shortwave radiation, together with absorption of longwave radiation radiated downward by greenhouse gases; heat carried away by ocean currents; and heat (including latent heat) lost to the atmosphere. Over the last 40 years, the tropical ocean surface has warmed by about 0.4 degrees Celsius (0.7 degrees Fahrenheit).

But the warming can’t be explained by rising CO₂ that went up from 341 ppm in 1982 to 417 ppm in 2022. This rise boosts the absorption of longwave radiation at the tropical surface by only 0.3 watts per square meter, according to the University of Chicago’s MODTRAN model, which simulates the emission and absorption of infrared radiation in the atmosphere. The calculation assumes clear sky conditions and tropical atmosphere profiles of temperature and relative humidity.

The 0.3 watts per square meter is too little to account for the increase in ocean surface temperature of 0.4 degrees Celsius (0.7 degrees Fahrenheit), which in turn increases the loss of latent and “sensible” (conductive) heat from the surface by about 3.5 watts per square meter, as estimated by Kininmonth.

So twelve times as much heat escapes from the tropical ocean to the atmosphere as the amount of heat entering the ocean due to the increase in CO₂ level. The absorption of additional radiation energy due to extra CO₂ is not enough to compensate for the loss of latent and sensible heat from the increase in ocean temperature.

The minimal contribution of CO₂ is evident from the following table, which shows how the amount of longwave radiation from greenhouse gases absorbed at the tropical surface goes up only marginally as the CO₂ concentration increases. The dominant greenhouse gas is water vapor, which produces 361.4 watts per square meter of radiation at the surface in the absence of CO₂; its value in the table (surface radiation) is the average global tropical value.

You can see that the increase in greenhouse gas absorption from preindustrial times to the present, corresponding roughly to the CO₂ increase from 300 ppm to 400 ppm, is 0.62 watts per square meter. According to the MODTRAN model, this is almost the same as the increase of 0.63 watts per square meter that occurred as the CO₂ level rose from 200 ppm to 280 ppm at the end of the last ice age – but which resulted in tropical warming of about 6 degrees Celsius (11 degrees Fahrenheit), compared with warming of only 0.4 degrees Celsius (0.7 degrees Fahrenheit) during the past 40 years.

Therefore, says Kininmonth, the only plausible explanation left for warming of the tropical ocean is a slowdown in ocean currents, those unseen arteries carrying the earth’s lifeblood of warmth away from the tropics. His suggested slowing mechanism is natural oscillations of the oceans, which he describes as the inertial and thermal flywheels of the climate system.

Kininmonth observes that the overturning time of the deep-ocean thermohaline circulation is about 1,000 years. Oscillations of the thermohaline circulation would cause a periodic variation in the upwelling of cold seawater to the tropical surface layer warmed by solar absorption; reduced upwelling would lead to further heating of the tropical ocean, while enhanced upwelling would result in cooling.

Such a pattern is consistent with the approximately 1,000-year interval between the Roman and Medieval Warm Periods, and again to current global warming.

Next: Ample Evidence Debunks Gloomy Prognosis for World’s Coral Reefs

Sudden Changes in Ocean Currents Warmed Arctic, Cooled Antarctic in Past

Abrupt changes in ocean currents – and not greenhouse gases – were responsible for sudden warming of the Arctic and for sudden cooling in the Antarctic at different times in the past, according to two recent research studies. The Antarctic cooling marked the genesis of the now massive Antarctic ice sheet.

The first study, by a team of European scientists, discovered that the expansion of warm Atlantic Ocean water flowing into the Arctic caused sea surface temperatures in the Fram Strait east of Greenland to rise by about 2 degrees Celsius (3.6 degrees Fahrenheit) as early as 1900. The phenomenon, known as “Atlantification” of the Arctic, is important because it precedes instrumental measurements of the effect by several decades and is not simulated by computer climate models.

The conclusion is based on an 800-year reconstruction of Atlantification along the Fram Strait, which separates Atlantic waters from the Arctic Ocean. The researchers used marine sediment cores as what they call a “natural archive” of past climate variability, deriving the chronological record from radionuclide dating.

Shown in the figure below is the sea surface temperature and Arctic sea ice extent from 1200 to 2000. The blue curve represents the reconstructed mean summer temperature (in degrees Celsius) of Atlantic waters in the eastern Fram strait, while the red curve indicates the April retreat (in kilometers) of the sea ice edge toward the Arctic. You can see clearly that the seawater temperature increased abruptly around 1900, after centuries of remaining constant, and that sea ice began to retreat at the same time, after at least a century of extending about 200 kilometers farther into the strait.

Along with temperature, the salinity of Atlantic waters in the strait suddenly increased also. The researchers suggest that this Atlantification phenomenon could have been due to weakening of two ocean currents – the AMOC (Atlantic Meridional Overturning Circulation) and the SPG (Subpolar Gyre), a circular current south of Greenland – at the end of the Little Ice Age. The AMOC forms part of the ocean conveyor belt that redistributes seawater and heat around the globe.

This abrupt change in ocean currents is thought to have redistributed nutrients, heat and salt in the northeast Atlantic, say the study authors, but is unlikely to be associated with greenhouse gases. The change caused subtropical Atlantic waters to flow northward through the Fram Strait, as illustrated schematically in the figure below; the halocline is the subsurface layer in which salinity changes sharply from low (at the surface) to high. The WSC (West Spitsbergen Current) carries heat and salt to the Arctic and keeps the eastern Fram Strait ice-free.

Sudden cooling occurred in the Antarctic but millions of years earlier, a second study has found. Approximately 34 million years ago, a major reorganization of ocean currents in the Southern Ocean resulted in Antarctic seawater temperatures abruptly falling by as much as 5 degrees Celsius (9 degrees Fahrenheit). The temperature drop initiated growth of the Antarctic ice sheet, at the same time that the earth underwent a drastic transition from warm Greenhouse to cold Icehouse conditions.

This dramatic cooling was caused by tectonic events that opened up two underwater gateways around Antarctica, the international team of researchers says. The gateways are the Tasmanian Gateway, formerly a land bridge between Antarctica and Tasmania, and Drake Passage, once a land bridge from Antarctica to South America. The scientists studied the effect of tectonics using a high-resolution ocean model that includes details such as ocean eddies and small-scale seafloor roughness.

After tectonic forces caused the two land bridges to submerge, the present-day ACC (Antarctic Circumpolar Current) began to flow. This circumpolar current, although initially less strong than today, acted to weaken the flow of warm waters to the Antarctic coast. As the two gateways slowly deepened, the warm-water flow weakened even further, causing the relatively sudden cooling event.

Little cooling occurred before one or both gateways subsided to a depth of more than 300 meters (1,000 feet). After the second gateway had subsided from 300 meters (1,000 feet) to 600 meters (2,000 feet), surface waters along the entire Antarctic coast cooled by 2 to 3.5 degrees Celsius (3.6 to 6.3 degrees Fahrenheit). And once the second gateway had subsided below 600 meters (2,000 feet), the temperature of Antarctic coastal waters decreased another 0.5 to 2 degrees Celsius (0.9 to 3.6 degrees Fahrenheit). The next figure depicts the gradual opening of the two gateways.

Although declining CO₂ levels in the atmosphere may have played a minor role, the study authors conclude that undersea tectonic changes were the key factor in altering Southern Ocean currents and in creating our modern-day Icehouse world.

Next: No Evidence That Thwaites Glacier in Antarctica Is about to Collapse

Challenges to the CO2 Global Warming Hypothesis: (5) Peer Review Abused to Axe Skeptical Paper

A climate research paper featured in a previous post of mine has recently been removed by the publisher, following a post-publication review by seven new reviewers who all recommended rejection of the paper. This drastic action represents an abuse of the peer review process in my opinion, as the reviews are based on dubious science.

The paper in question was a challenge to the CO₂ global warming hypothesis by French geologist Pascal Richet. From analysis of an Antarctic ice core, Richet postulates that greenhouse gases such as CO₂ had only a minor effect on the earth’s climate over the past 423,000 years, and that any assumed forcing of climate by CO₂ is incompatible with ice-core data.

Past atmospheric CO₂ levels and surface temperatures are calculated from ice cores by measuring the air composition and the oxygen ¹⁸O to ¹⁶O isotopic ratio, respectively, in air bubbles trapped by the ice. Data from the core, drilled at the Russian Vostok station in East Antarctica, is depicted in the figure below. The CO₂ level is represented by the upper graphs (below the insolation data) that show the substantial drop in CO₂ during an ice age; the associated drop in temperature ΔT is represented by the lower graphs.

It’s well known that the CO₂ level during the ice ages closely mimicked changes in temperature, but the CO₂ concentration lagged behind. What Richet observed is that the temperature peaks in the Vostok record are much narrower than the corresponding CO₂ peaks. From this observation, he argued that CO₂ can’t drive temperature since an effect can’t last for a shorter period than its cause.

The seven negative reviews focused on two main criticisms. The first is that Richet supposedly fails to understand that CO₂ can act both as a temperature driver, when CO₂ leads, and as an amplifying feedback, when CO₂ lags.

At the end of ice ages, it’s thought that a subtle change in the earth’s orbit around the sun initiated a sudden upward turn of the temperature. This slight warming was then amplified by feedbacks, including CO₂ feedback triggered by a surge in atmospheric CO₂ as it escaped from the oceans; CO₂ is less soluble in warmer water. A similar but opposite chain of events is believed to have enhanced global cooling as the temperature fell at the beginning of an ice age. In both cases – deglaciation and glaciation – CO₂ as a feedback lagged temperature.

However, several of Richet’s reviewers base their criticism on a 2012 paper, by paleoclimatologist Jeremy Shakun and coauthors, which proposes the somewhat preposterous notion that CO₂ lagged temperature during the most recent glaciation, all through the subsequent ice age, and during 0.3 degrees Celsius (0.5 degrees Fahrenheit) of the initial warming as the ice age ended – but then switched roles from feedback to driver and led temperature during the remaining deglaciation.

Shakun’s proposal is illustrated in the left graph below, in which the blue curve shows the mean global temperature during deglaciation, the red curve represents the temperature in Antarctica and the yellow dots are the atmospheric CO₂ concentration. The CO₂ levels and Antarctic temperatures are derived from an ice core, as in Richet’s paper but using the so-called Dome C core, while global temperatures are calculated from proxy data obtained from ocean and lake sediments.

The apparent switch of CO₂ from feedback to driver is clearly visible in the figure above about 17,500 years ago, when the temperature escalated sharply. Although the authors attempt to explain the sudden change as resulting from variability of the AMOC (Atlantic Meridional Overturning Circulation), their argument is only hand-waving at best and does nothing to bolster their postulated dual role for CO₂.

In any case, a detailed, independent analysis of the same proxy data has found there is so much data scatter that whether CO₂ leads or lags the warming can’t even be established. This analysis is shown in the right graph above, where the green dots represent the temperature data and the black circles are the CO₂ level.

All this invalidates the reviewers’ first main criticism of Richet’s paper. The second criticism is that Richet dismisses computer climate models as an unreliable tool for studying the effect of CO₂ on climate, past or present. But, as frequently pointed out in these pages, climate models indeed have many weaknesses. These include the omission of many types of natural variability, exaggeration of predicted temperatures and the inability to reproduce the past climate accurately. Repudiation of climate models is therefore no reason to reject a paper.

Some of the reviewers’ lesser criticisms of Richet’s paper are justified, such as his analysis of only one Antarctic ice core when several are available, and his inappropriate philosophical and political comments in a scientific paper. But outright rejection of the paper smacks of bias against climate change skeptics and is an abuse of the time-honored tradition of peer review.

Next: The Crucial Role of Water Feedbacks in Global Warming

Ice Sheet Update (2): Greenland Ice Sheet Melting No Faster than Last Century

The climate doomsday machine makes much more noise about warming-induced melting of Greenland’s ice sheet than Antarctica’s, even though the Greenland sheet holds only about 10% as much ice. That’s because the smaller Greenland ice sheet is melting at a faster rate and contributes more to sea level rise. But the melt rate is no faster today than it was 90 years ago and appears to have slowed over the last few years.

The ice sheet, 2-3 km (6,600-9,800 feet) thick, consists of layers of compressed snow built up over at least hundreds of thousands of years. Melting takes place only during Greenland’s late spring and summer, the meltwater running over the ice sheet surface into the ocean, as well as funneling its way down through thick glaciers, helping speed up their flow toward the sea.

In addition to summer melting, the sheet loses ice at its edges from calving or breaking off of icebergs, and from submarine melting by warm seawater. Apart from these losses, a small amount of ice is gained over the long winter from the accumulation of compacted snow at high altitudes in the island’s interior. The net result of all these processes at the end of summer melt in August is illustrated in the adjacent figure, based on NASA satellite data.

The following figure depicts the daily variation, over the past year, of the estimated surface mass balance of the Greenland ice sheet – which includes gains from snowfall and losses from melt runoff, but not sheet edge losses – as well as the mean daily variation for the period from 1981 to 2010. The loss of ice during the summer months of June, July and August is clearly visible, though the summer loss was smaller in 2021 than in many years. An unusual, record-setting gain can also be seen in May 2021.

The next figure shows the average annual gain or loss of both the surface mass balance (in blue) and a measure of the total mass balance (in black), going all the way back to 1840. Most of the data comes from meteorological stations across Greenland. The total mass balance in this graph includes the surface mass balance, iceberg calving and submarine melting (combined in the gray dashed line), and melting from basal sources underneath the ice sheet, but not peripheral glaciers – glaciers that contribute 15 to 20% of Greenland’s total mass loss.

It can be seen that the rate of ice loss excluding glaciers has increased since about 2000. But it’s also clear from the graph that high short-term loss rates have occurred more than once in the past, notably in the 1930s and the 1950s – so the current shrinking of the Greenland ice sheet is nothing remarkable. There’s no obvious correlation with global temperatures, since the planet warmed from 1910 to 1940 but cooled from 1940 to 1970.

The total ice loss (not its rate) since 1972 is displayed in more detail in the final figure below. The slightly different estimates of the total mass are because some estimates include losses from peripheral glaciers and basal melting, while others don’t. Nevertheless, the insert showing mass loss from 2010 to 2020 reveals clearly that the rate of loss may have slowed down since about 2015.

The 2020 loss was 152 gigatonnes (168 gigatons), much lower than the average annual losses of 258 gigatonnes (284 gigatons) and 247 gigatonnes (272 gigatons) from 2002 to 2016 and 2012 through 2016, respectively. The 2020 loss also pales in comparison with the record high losses of 458 gigatonnes (505 gigatons) in 2012 and 329 gigatonnes (363 gigatons) in 2019. The 2021 loss is on track to be similar to 2020, according to estimates at the end of the summer melt season.

The Sixth Assessment Report of the UN’s IPCC (Intergovernmental Panel on Climate Change) maintains with high confidence that, between 2006 and 2018, melting of the Greenland ice sheet and peripheral glaciers was causing sea levels to rise by 0.63 mm (25 thousandths of an inch) per year. This can be compared with a rise of 0.37 mm (15 thousandths of an inch) per year from melting of Antarctic ice. However, the rate of rise from Greenland ice losses may be falling, as discussed above.

If the rate of Greenland ice loss were to remain at its 2012 to 2016 average of 247 gigatonnes (272 gigatons) per year, which is an annual loss of about 0.01% of the total mass of the ice sheet, it would take another 10,000 years for all Greenland’s ice to melt. If the rate stays at the 2020 value of 152 gigatonnes (168 gigatons) per year, the ice sheet would last another 17,000 years.

Next: Challenges to the CO2 Global Warming Hypothesis: (5) Peer Review Abused to Axe Skeptical Paper

Challenges to the CO2 Global Warming Hypothesis: (4) A Minimal Ice-Age Greenhouse Effect

As an addendum to my 2020 series of posts on the CO₂ global warming hypothesis (here, here and here), this post presents a further challenge to the hypothesis central to the belief that humans make a substantial contribution to climate change. The hypothesis is that observed global warming – currently about 1 degree Celsius (1.8 degrees Fahrenheit) since the preindustrial era – has been caused primarily by human emissions of CO₂ and other greenhouse gases into the atmosphere.

The new challenge to the CO₂ hypothesis is set out in a recent research paper by French geologist Pascal Richet. Richet claims, by reexamining previous analyses of an Antarctic ice core, that greenhouse gases such as CO₂ and methane had only a minor effect on the earth’s climate over the past 423,000 years, and that the assumed forcing of climate by CO₂ is incompatible with ice-core data. The paper is controversial, however, and the publisher has subjected it to a post-publication review, as a result of which the paper has since been removed.

The much-analyzed ice core in question was drilled at the Russian Vostok station in East Antarctica. Past atmospheric CO₂ levels and surface temperatures are calculated from ice cores by measuring the air composition and the oxygen ¹⁸O to ¹⁶O isotopic ratio, respectively, in air bubbles trapped by the ice. The Vostok record, which covers the four most recent ice ages or glaciations as well as the current interglacial (Holocene), is depicted in the figure below. The CO₂ level is represented by the upper set of graphs (below the insolation data), and shows the substantial drop in CO₂ during an ice age; the associated drop in temperature ΔT is represented by the lower set of graphs.

It is seen that transitions from glacial to interglacial conditions are relatively sharp, while the ice ages themselves are punctuated by smaller warming and cooling episodes. And, though it’s hardly visible in the figure, the ice-age CO₂ level closely mimics changes in temperature, but the CO₂ concentration lags behind – with CO₂ going up or down after the corresponding temperature shift occurs. The lag is more pronounced for temperature declines than increases.

The oceans, which are where the bulk of the CO₂ on our planet is stored, can hold much more CO₂ (and heat) than the atmosphere. Warm water holds less CO₂ than cooler water, so the oceans release CO₂ when the temperature rises, but take it in when the earth cools.

Richet noticed that the temperature peaks in the Vostok record are much narrower than the corresponding CO₂ peaks. The full widths at half maximum, marked by thick horizontal bars in the figure above, range from about 7,000 to 16,000 years for the initial temperature peak in cycles II, III and IV, but from 14,000 to 23,000 years for the initial CO₂ peak; cycle V can’t be analyzed because its start is missing from the data. All other peaks are also narrower for temperature than for CO₂.

The author argues that CO₂ can’t drive temperature since an effect can’t last for a shorter period of time than its cause. The fact that the peaks are systematically wider for CO₂ than for temperature implies that the CO₂ level responds to temperature changes, not the other way round. And for most of cycles II, III and IV, CO₂ increases correspond to temperature decreases and vice versa.

Richet’s conclusion, if correct, would deal a deathblow to the CO₂ global warming hypothesis. The reason has to do with the behavior of the temperature and CO₂ level at the commencement and termination of ice ages.

Ice ages are believed to have ended (and begun) because of changes in the Earth’s orbit around the sun. After tens of thousands of years of bitter cold, the temperature suddenly took an upward turn. But according to the CO₂ hypothesis, the melting of ice sheets and glaciers caused by the slight initial warming could not have continued, unless this temperature rise was amplified by positive feedbacks. These include CO₂ feedback, triggered by a surge in atmospheric CO₂ as it escaped from the oceans.

The problem with this explanation is that it requires a similar chain of events, based on CO₂ and other feedbacks, to have enhanced global cooling as the temperature fell at the beginning of an ice age. But, says Richet, “From the dual way in which feedback would work, temperature decreases and increases should be similar for the same concentrations of greenhouse gases, regardless of the residence times of these gases in the atmosphere.” The fact that temperature decreases don’t depend in any straightforward way on CO₂ concentration in the figure above demonstrates that the synchronicity required by the feedback mechanism is absent.

Next: Fishy Business: Alleged Fraud over Ocean Acidification Research, Reversal on Coral Extinction

What Triggered the Ice Ages? The Uncertain Role of CO2

About a million years ago, the earth’s ice ages became colder and longer – with a geologically sudden jump from thinner, smaller glaciers that came and went every 41,000 years to thicker, larger ice sheets that persisted for 100,000 years. Although several hypotheses have been put forward to explain this transition, including a long-term decline in the atmospheric CO₂ level, the phenomenon remains a scientific conundrum.

Two research teams spearheaded by geologists from Princeton University have recently described their attempts to resolve the mystery. A 2019 study measured the CO₂ content in two-million-year-old ice cores extracted from Antarctica, which are by far the oldest cores ever recovered and span the puzzling transition to a 100,000-year ice age cycle that occurred a million years before. A just reported 2020 study utilized seabed sediment cores from the Antarctic Ocean to investigate storing of CO₂ in the ocean depths over the last 150,000 years.

Both studies recognize that the prolonged deep freezes of the ice ages are set off partly by perpetual but regular changes in the earth’s orbit around the sun. That’s the basis of a hypothesis proposed by Serbian engineer and meteorologist Milutin Milankovitch. As shown in the figure below, the earth orbits the sun in an elliptical path and spins on an axis that is tilted. The elliptical orbit stretches and contracts over a 100,000-year cycle (top), while the angle of tilt or obliquity oscillates with a 41,000-year period (bottom), and the planet also wobbles on its axis in a 26,000-year cycle (center).

Milankovitch linked all three cycles to glaciation, but his hypothesis has been dogged by two persistent problems. First, it predicts a dominant 41,000-year cycle governed by obliquity, whereas the current pattern is ruled by the 100,000-year eccentricity cycle as mentioned above. Second, the orbital fluctuations thought to trigger the extended cooling cycles are too subtle to cause on their own the needed large changes in solar radiation reaching the planet – known as insolation. That’s where CO₂ comes in, as one of various feedbacks that amplify the tiny changes that do occur.

Before the 2019 Princeton study, it had been suspected that the transition from 41,000-year to 100,000-year cycles was due to a long-term decline in the atmospheric CO₂ level over both glacial and interglacial epochs. But that belief held when ice-core data went back only about 800,000 years. Armed with their new data from 2 million years in the past, the first Princeton team discovered surprisingly that the average CO₂ level was unchanged over that time span, even though the minimum level dropped after the transition to longer ice age cycles.

This means that the 100,000-year transition can’t be attributed to CO₂, although CO₂ feedback has been invoked to explain the relatively sudden temperature rise at the end of ice ages. Rather, said the study authors, the switch in ice age length was probably caused by enhanced growth of ice sheets or changes in global ocean circulation.

It’s another feedback process involving CO₂ that was investigated by the second Princeton team, who made measurements on tiny fossils embedded in Antarctic Ocean sediments. While it has long been known that the atmospheric CO₂ level and global temperatures varied in tandem over glacial cycles, and that CO₂ lagged temperature, the causes of the CO₂ fluctuations are not well understood.

We know that the oceans can hold more CO₂ than the atmosphere. Because CO₂ is less soluble in warm water than cooler water, CO₂ is absorbed from the atmosphere by cold ocean water at the poles and released by warmer water at the equator. The researchers found that, during ice ages, the Antarctic Ocean stored even more CO₂ than expected. Absorption in the Antarctic is enabled by the sinking of floating algae that carry CO₂ deep into the ocean before becoming fossilized, a process referred to as the "biological carbon pump."

But some of the sequestered CO₂ normally escapes, due to the strong eastward winds encircling Antarctica that drag CO₂-rich deep water up to the surface and vent the CO₂ back to the atmosphere. The new research provides evidence that this wind-driven Antarctic Ocean upwelling slowed down during the ice ages, allowing less CO₂ to be vented and more to remain locked up in the ocean waters.

Apart from any effect this retention of CO₂ may have had on ice-age temperatures, the researchers say their data suggests that the past lag of CO₂ behind temperature may have been caused directly by the effect on Antarctic upwelling of changing obliquity in the earth’s orbit – Milankovitch’s 41,000-year cycle. The study authors believe this explains why the eccentricity and precession cycles now prevail over the obliquity cycle.

Next: Both Greenland and Antarctic Ice Sheets Melting from Below