Brocken Inaglory/Wikimedia Commons

Irreversible does not mean unavoidable when it comes to climate change. Although we're committed to the damage from past carbon dioxide increases, steps to cut carbon emissions today would start to affect the rate of future global warming immediately.

In a “Perspectives” article in the journal Science, two scientists (Damon Matthews and Susan Solomon) say that the inevitability of future warming if carbon dioxide emissions remain fixed at current levels has been misinterpreted. It does not mean that the rate of increase in Earth’s global temperature is inevitable; it may change based on how much or how quickly emissions decrease.

Earth’s climate warms in response to increases in atmospheric carbon dioxide concentrations, which result from burning fossil fuels, clearing land, and certain industrial and manufacturing processes. The carbon dioxide allows visible light to reach the Earth, but absorbs infrared light that would otherwise escape to space. The atmosphere's warming can be slowed by heat storage in the ocean, but that slow transport of heat generally means there's a lag—longer time periods are required for changes to be seen in the atmosphere.

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Lawrence Livermore National Lab

It's been five years since the last report from the Intergovernmental Panel on Climate Change, and the organization is currently preparing its fifth assessment report (AR5). These reports provide both an update on what we've learned about the climate in the intervening years and projections for likely future climates based on that new understanding.

Those projections are powered by climate models. Starting with AR4, those projections were based on the work of the World Climate Research Programme. This group identifies the current climate models from a variety of institutions, and runs them under a variety of emissions scenarios. Then, the WCRP collects the results of multiple runs from the ensemble of climate models, and uses that to predict the likely climate change and remaining uncertainties.

You might expect the progress made during the intervening five years would greatly narrow the uncertainties since the last report. If so, get ready for disappointment. A pair of researchers from ETH Zurich has compared the results from AR4 with the ones that will be coming out in AR5, and they find that the uncertainties haven't gone down much. And, somewhat ironically, they blame the improvements—as researchers are able to add more factors to their models, each new factor comes with its own uncertainties, which keeps the models from narrowing in on a value.

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Enlarge / The gray areas are one and two standard deviations from the calculated temperature (black line). The other surface temperature records are colored red, green, and blue.

Berkeley Earth

Despite plenty of indications that the Earth has gotten warmer—like melting glaciers and ecosystems that are shifting toward the poles—there are a number of climate skeptics who simply don't accept the temperature records produced by three different organizations (NASA, NOAA, and the CRU). Many of them pinned their hopes on physicist Richard Muller, who was also not convinced the professionals had gotten it right. But Muller did something about it, forming the Berkeley Earth project, and building a huge database of land temperature records.

Back in October, Muller dropped his findings in a rather unconventional location: an editorial in The Wall Street Journal. Despite the hype, the results were rather bland. He produced a temperature record that was nearly identical to that of the other organizations. But now, Muller is back for round two, and this time he has chosen the New York Times as an outlet for his climate musings.

As before, his team uses a different statistical method of reconstructing temperatures that works well with short records, taken at sites that were shut or moved. NASA, NOAA, and the CRU use methods that require long records, so they have to make adjustments to the data from sites that have shifted or gotten new equipment. This compensates for the fact that these changes will lead to discontinuities in the record. Since Berkeley Earth doesn't need the same length, it can just skip adjustments entirely: any record with a discontinuity is just split there, and treated as two records. The team has now also pushed its analysis back to almost 1750, adding a century to the land temperature records produced elsewhere.

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