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The weather reports are in. 2012 was the hottest and the most extreme year on record in many places.

While parts of China are enduring the harshest winter in 30 years, the Antarctic is warming at an alarming rate. In Australia, out-of-control bushfires are partially the result of record-breaking weather (new colors were added to weather forecast maps, to account for the new kind of heat). In the United States, where Hurricane Sandy devastated parts of New Jersey and New York and where extreme drought still lingers in the Midwest, the average temperature in 2012 was more than a whole degree Fahrenheit (or 5/9 of a degree Celsius) higher than average – shattering the record.

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On Friday a long-term weather forecast for the United States was released, when the National Climate Assessment and Development Advisory Committee published a draft of the third Climate Assessment Report. Like last year’s weather, the assessment does not pull its punches.

“Climate change threatens human health and well-being in many ways, including impacts from increased extreme weather events, wildfire, decreased air quality, diseases transmitted by insects, food, and water, and threats to mental health,” write the authors as part of their key findings.

Experts from 13 federal agencies, including NASA, the State Department and the Department of Defense put together the report under the auspices of the United States Global Change Research Program.

While some predictions have been adjusted upward from previous reports, the difference in tone in this newest assessment is striking. The second assessment, published in 2009, predicted thresholds that will be crossed, while the 2013 draft presents a reality in which some of the changes are already irreversible.

“As a result of past emissions of heat-trapping gases, some amount of additional climate change and related impacts is now unavoidable,” wrote the authors in the executive summary.

Adaptation to climate change is discussed in the new draft, which is open for public comment before it is officially released early in 2014. The authors write:

Planning and managing based on the climate of the last century means that tolerances of some infrastructure and species will be exceeded. For example, building codes and landscaping ordinances will likely need to be updated not only for energy efficiency, but also to conserve water supplies, protect against insects that spread disease, reduce susceptibility to heat stress, and improve protection against extreme events.

The authors predict that within the next several decades, temperatures will go up between 2 and 4 degrees Fahrenheit, roughly 1 and 2 degrees Celsius. The experts discuss a possible 10 degree Fahrenheit (or more than 5 degrees Celsius) warming by the end of the century, in the case that not enough is done to curb emissions. (The World Bank recently released a report of the dangers of a world warmed by 4 degrees Celsius).

Sea levels could rise up to four feet, or 1.2 meters, within the century, according to the experts.

Though official assessments, predictions and studies like these serve to reinforce what many already fear, they do not necessarily lead to policy change. Andrew Restuccia predicted in a Politico article that the new report would ultimately do little to change the embittered climate-change politics in that country. He wrote:

But don’t hold your breath for serious action on climate change in Congress. Republicans and some moderate Democrats remain opposed to measures to address climate change. The Obama administration, meanwhile, is moving forward with its own efforts on climate change, including beefed-up fuel economy standards and greenhouse gas regulations for new power plants.

Sometimes official assessment reports provide substance for those who question man-made climate change.

My colleague Andrew C. Revkin recently reported on how a revision by Britain’s Weather and Climate Agency on short-term global temperature forecast became fodder for climate change deniers. The fact that the government agency had revised its numbers downward allowed climate change skeptics to argue that the world was not significantly warming after all.

In December, Alec Rawls, a climate-change skeptic, made a name for himself by leaking an unpublished Assessment Report from the Intergovernmental Panel on Climate Change, one of the major global players in climate change assessment. Mr. Rawls tried to argue that the panel’s language on solar radiation was an admission that much of the warming trends were caused by the sun, not human activity.

As Andrew reported at time, his claims were mostly debunked.