A Year’s End Climate Reflection: Approaching the Climate Cliff

Emissions continue to trend up. Is it too late to avoid a temperature rise of 2 degrees Celsius (3.6 degrees Fahrenheit)?

Since 1992, the end of the year has marked something of a bitter irony. Coinciding with the early release of annual greenhouse gas emissions data is the annual climate confab known as the COP (short for Conference of the Parties, an association of countries that make up the UN Framework Convention on Climate Change, the international pledge to keep climate change in check). This year is no exception.

Much like previous COPs, the negotiators who are heading home from the COP18 held in Doha, Qatar, have agreed to put off agreeing on what a post-Kyoto plan will look like. After all, next year is another year. (Read more about COP18.) At the same time, we learn that once again global carbon dioxide (CO2) emissions continue to increase — emissions during 2012 are expected to have grown by about 2.6 percent above last year’s number, totaling about 35.6 ±1.8 billion tons carbon. In fact, since 2000, global CO2 emissions have grown at an average annual rate of 3.1 percent. (More on CO2 levels here.)

It’s a drag, as we used to say back in the day. While the whole point of the COP climate conferences is to find a way to reduce greenhouse gas emissions to avoid dangerous climate interference — the so-called goal of no more than a “2 degree Celsius” rise — the 2012 emissions tally emphatically underscores that whatever it is we’re doing ain’t working.

The window to act: sooner rather than later

That’s bad enough, but get this.

Writing in the journal Nature Climate Change last week, Glen Peters of the Center for International Climate and Environmental Research in Oslo and colleagues point out that the CO2 emissions over the past three decades have been tracking the high end of the emission scenarios, which are used by the Intergovernmental Panel on Climate Change (the leading international scientific body tasked with studying climate change) to make climate projections.

Peters et al go on to suggest that we need to act quickly to reverse this trend if we are to keep the average global temperature below the 2 degree C rise.

“Significant emission reductions are needed by 2020 to keep 2 °C as a feasible goal. … [And this] requires sustained global CO2 mitigation rates of around 3% per year, if global emissions peak before 2020. A delay in starting mitigation activities will lead to higher mitigation rates, higher costs, and the target of remaining below 2 °C may become unfeasible.”

A similar warning is sounded by Michael Schlesinger and colleagues from the University of Illinois at Urbana-Champaign. Writing in the Journal of Environmental Protection in June 2012, the authors conclude in a paper entitled “A Fair Plan to Safeguard the Earth’s Climate”* that, to avoid the 2 degree C threshold, all countries would need to begin reducing emissions by 2015 and bring those emissions to zero by 2065. A tall order, to put it mildly — and, given that 2013 is around the corner (putting 2015 a mere two years away), one that seems highly unlikely to be met. Indeed, the current UNFCCC plan is to have a new global climate treaty in place by 2020.

The wiggle room on the timeline to act

Now, these very same authors have given the planet a reprieve. Perhaps recognizing the impossibility of beginning emissions reductions by 2015, they wrote in the same journal in October a follow-on to their June paper where they examine whether it is possible to miss the 2015 start year and still stay below a rise of 2 degrees C. And their answer is yes … well, a qualified yes.

Schlesinger et al do show a set of model simulations in which we wait until 2020 (instead of 2015) to begin reducing emissions and take as long as 80 years to bring emissions to zero and still keep the average global temperature increase below the 2 degree Celsius threshold. This would shift peak emissions from developed countries from 2015 to 2030 and for developing countries from 2042 to 2053.

How did Schlesinger and his co-authors manage to do this? They did it by carrying out their simulations in a model world where the climate sensitivity is set at the low end of its estimated range. Current estimates hold that the climate sensitivity — the global temperature change from a doubling of CO2 — ranges from about 2 to 4.5 degrees C (3.6 to 8 degrees F). Schlesinger et al assume the climate sensitivity to be only 1.45 to 2 degrees C (2.6 to 3.6 degrees F).

Why did the authors assume a low climate sensitivity? For that you need to go to yet another paper. The lead author on this one is Michael Ring (one of the co-authors on the two Schlesinger et al papers discussed above). In this paper the authors compare observed and model-calculated temperatures over 160 years, from 1850 to 2010. Their major conclusion is that greenhouse gas emissions are the primary cause of warming global temperatures beginning in 1976. However, their second conclusion is that the climate sensitivity is at the low end of the estimated range.

So, by assuming a low climate sensitivity in their model world, Schlesinger et al find that there is more time to get serious about lowering emissions. But alas, that’s a model world. What about the actual world? Does the lower climate sensitivity still apply? It’s not possible to say definitively. There have been a number of other estimates of the climate sensitivity of late — and a number of them (including this one and this one) have fallen at the high end of the estimated range. And truth be told, even having until 2020 to begin lowering emissions will be no walk in the park.

Still, in a year that has been filled with bleak weather and climate news (see a sampling here, here, here and here), this paper by Ring and colleagues is like a welcome, end-of-the year holiday present. I for one am going to treat it as such.


End Note

The plan is deemed “fair” because it hopes to lay out a framework to allow developing countries to begin reducing emissions more slowly, but requires each group to make the same cumulative emission reductions before emissions are reduced to zero.

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