Latest Study Shows Earth Is At Its Hottest In 120,000 Years

A new study shows the Earth is on track to be warmer than it has been in about 120,000 years, and is locked into eventually hitting its hottest mark in more than 2 million years. Carolyn Snyder, as part of her doctoral dissertation at Stanford University (she's now a climate policy official at the EPA)), created a continuous 2 million year temperature record, much longer than a previous 22,000 year record. Snyder’s temperature reconstruction, published Monday in the journal Nature, doesn’t estimate temperature for a single year, but averages 5,000-year time periods going back a couple million years.

Snyder based her reconstruction on 61 different sea surface temperature proxies from across the globe, such as:  ratios between magnesium and calcium (Mg/Ca), species makeup and acidity. But the further the study goes back in time, especially after half a million years, the fewer of those proxies are available, making the estimates less certain, she said. Snyder, unlike the climate change deniers, also acknowledged her estimates are rough with large uncertainties. But she also found that the temperature changes correlated well to carbon dioxide levels.

Snyder found that temperatures averaged out over the most recent 5,000 years — which includes the last 125 years or so of industrial emissions of heat-trapping gases — to be generally warmer than they have been since about 120,000 years ago. Also, two interglacial time periods, the one 120,000 years ago and another just about 2 million years ago, were the warmest Snyder tracked. They were about 3.6 degrees (2 degrees Celsius) warmer than the current 5,000-year average.

Using the link to carbon dioxide levels and taking into account other factors and past trends, Snyder calculated how much warming can be expected in the future. Assuming climate factors are the same as in the past, she found that Earth is  headed for 7 degrees (about 4 degrees Celsius) of warming over the next few thousand years. Lest anyone believe this is incomprehensible, let's recall a Reuters report from July, 2010:

"the Met Office Hadley Centre and other climate research centres  imposed (a projection of 4C temperature increase) on to a Google Earth layer. It's a timely arrival, with warnings this month that current international carbon pledges will lead to a rise of nearly 4C ."


Google maps projection of 4C greenhouse world  - showing from five years ago that Snyder's figures are in the ballpark for realistic expectations.

Meanwhile, a Guardian UK article from May 17, 2015 bluntly pointed out:

"A paper used for guiding future business planning at the Anglo-Dutch multinational assumes that carbon dioxide emissions will fail to limit temperature increases to 2C, the internationally agreed threshold to prevent widespread flooding, famine and desertification. Instead, the New Lens Scenarios document refers to a forecast by the independent International Energy Agency (IEA) that points to a temperature rise of up to 4C in the short term, rising later to 6C."

The message?  Given that once a runaway threshold is hit (which it likely will be once we pass 4C and continue to 6C)  these numbers will settle into a permanently heated planet- inexorably leading to the condition of a second Venus. See e.g.

http://brane-space.blogspot.com/2012/08/how-did-once-good-planet-go-bad.html


In other words, all the quibbles aside, Carolyn Snyder's figures are definitely plausible, and may even be too low, given the Hadley,, IEA findings disclose a 4C rise by 2100. Snyder herself observed:

“This is based on what happened in the past, In the past it wasn’t humans messing with the atmosphere.”

Yes, well it was mainly  volcanoes - but even now they can't compare to humans. A good parameter is the "ACM multiplier" (cf. Volcanic Versus Anthropogenic Carbon Dioxide in Eos: Transactions of the American Geophysical Union( Vol. 92, No. 24, June 14, 2011, p. 201)   The essential data of the paper is shown in the accompanying graph, for which the dots show a time series of the anthropogenic carbon dioxide CO2 multiplier (ACM) calculated from time series data on anthopogenic CO2 emission rates and Marty & Tolstikhin's (1998) study of preferred volcanic emission rates.

In their paper appearing in Chemical Geology (Vol. 145, p. 233) the latter authors gave a preferred estimate of 0.26 gigaton per year for present day global volcanic emission rate and injection. Their study encompassed CO2 emissions from divergent tectonic plates, intraplates (plumes) and convergent plates - e.g. displaying volcanism.

Moreover as the Eos paper observes, their computations "assessed the highest preferred minimum and maximum global estimates, making them appropriate high end volcanic limits for the comparisons with anthropogenic CO2 emissions covered with in this article".

To that extent, the Eos author (Terry Gerlach of the U.S. Geological Survey)showed from his time series that the projected anthropogenic CO2 emission rate of 35 gigatons per year is 135 times greater than the 0.26 gigatons per year emission rate for volcanoes, plumes etc. This ratio of 135:1 (anthropogenic to volcanic CO2) is what defines the anthropogenic multiplier, an index of anthropogenic CO2's dominance over volcanic inputs.

It is also worth mentioning how the ACM data show an astounding rise in the CO2 multiplier from about 18 in 1900, to roughly 38 in 1950, which parallels the vastly enhanced use of automobiles as a primary mode of personal transport - with the planet now saddled with nearly 600 million vehicles! Every manjack in a third world nation even seeks to own one!

Interestingly the only volcanic event which even came close to human emissions in the last several decades  was the eruption of Mt. Pinatubo in the Philippines in 1992. It generated CO2 emission rates roughly between 0.001 and 0.006 gigaton per hour, or closely approximating to the 0.004 gigaton anthropogenic per hour (e.g. based on 35 gigatons per year).Thus, as the Eos article observes:

For a few hours individual volcanoes may emit as much or more CO2 than human activities. But volcanic emissions are ephemeral while anthropogenic CO2 is emitted relentlessly from from ubiquitous sources..

Which means human activity is a vastly more significant source of CO2 and the major reason we are approaching a CO2 concentration (taken to be from 550- 600 ppm)that marks the threshold to the runaway greenhouse effect.

Scientists have given various reasons for past changes in carbon dioxide and heat levels, including regular slight shifts in Earth’s axial tilt. But on the evidence, including the work done by Prof. Gunter Weller in the 1980s at the University of Alaska-Fairbanks, it now appears increased CO2 from carbon combustion dwarfs all other factors.

Prof. Gunther Weller at the Geophysical Institute - UAF, ca. 1986

Prof. Weller first presented this in his detailed ice core measurements in a 1987  research report and showed that the Arctic temperatures (then) were some 7F warmer than rest of the world. The ice cores available at his Atmospheric Physics lab (part of the Geophysical Institute in Fairbanks) were extracted from Arctic ice at depths corresponding with geological time frames dating back over 80,000 years. His results showed that the greatest ambient temperatures corresponded to the highest CO2 concentrations in the ice cores. Also the largest increases in ambient temperatures have occurred over the past 50-60 years, during which the CO2 increases have been largest. Since then this relationship has only been further corroborated.

Flash forward now and at least four outside scientists praised the Snyder study’s tracking of past temperatures, with assorted caveats that its becomes less certain it is as one gets deeper in the past. Jeremy Shakun of Boston College said “Snyder’s work is a great contribution and future work should build on it.”

But many of the same scientists said Snyder’s estimate of future warming seems "too high". Shakun called it unrealistic and not matching historical time periods of similar carbon dioxide levels. But the point he is missing is that this isn't a "similar period for CO2 levels". (Especially given greenhouse gases such as methane- with even higher forcing factors-  are now increasing at even faster rates than CO2.)  See e.g

http://brane-space.blogspot.com/2015/05/methane-release-increases-because-of.html

 Outgassed methane, say from melting permafrost, delivers roughly the same forcing (nonlinear)  'punch' in 20-25 years that CO2 does in 100 years. Prof. Weller's own Arctic measurements project a melting Arctic and runaway greenhouse onset within a century. And once the runaway threshold is hit there is no turning back, there will be no going back to "ice ages".  The point? Extended five thousand or two million year records will be impossible to assess anyway because no humans will be around to do it! The runaway greenhouse effect will take out human civilization, making it an extended "extinction event" as real as a Torino 9 asteroid strike.  So if there are any "caveats"  they ought to focus on the uncertainties in Snyder's past record assembly, but not her temperature projections going forward.

Michael Mann of Pennsylvania State University, called the study "provocative and interesting" but said he remains skeptical until more research confirms it.  I believe more research has done that, as with Weller's work and also the forecasts of the Hadley UK Met Office and the  International Energy Agency.   Mann found the future temperature calculations “so much higher than prevailing estimates that one has to consider it somewhat of an outlier.”

But my 0.02, and I admit I am not an atmospheric physicist (but I do plow through many climate papers), is that it is smack square in the realm of realistic expectations, so not an "outlier" at all as we will soon see in the coming decade.