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The IPCC’s New Climate Science Guide for the Perplexed Policymaker

It is remarkable how many U.S. elected officials appear to be baffled about climate change these days. Despite the long scientific consensus that emissions of heat-trapping gases from burning fossil fuels and other human activities are driving disruptive changes to Earth’s climate, “I am not a scientist” has recently become the response that some members of Congress, governors, and other politicians are now giving to questions about whether they think climate change is a problem.

If you are a confused policymaker, perhaps fearful of answering the question incorrectly, fear no longer. The world’s leading climate scientists have just created a handy guide for you. On Sunday, the Intergovernmental Panel on Climate Change (IPCC) released its Fifth Assessment Synthesis Report’s Summary for Policymakers, distilling thousands of peer-reviewed scientific papers characterizing the latest information on climate science, impacts, and solutions into just forty pages of text and graphics. The IPCC further distilled these findings into some headlines – barebone facts that any policymaker should know.

Here are ten top-line findings:

Human influence on the climate system is clear and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems.

Warming of the climate system is unequivocal and since the 1950’s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.

Anthropogenic greenhouse gas emissions have increased since the pre-industrial era…and are now higher than ever. This has led to atmospheric concentrations of carbon dioxide, methane and nitrous oxide that are unprecedented in at least the last 800,000 years. 

Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems.

Limiting climate change would require substantial and sustained reductions in greenhouse gas emissions which, together with adaptation, can limit climate change risks.

It is very likely that heat waves will occur more often and last longer, and that extreme precipitation events will become more intense and frequent in many regions. The ocean will continue to warm and acidify, and global mean sea level to rise.

Climate change… risks…are generally greater for disadvantaged people and communities in countries at all levels of development.

Substantial emissions reductions over the next few decades can reduce climate risks in the 21st century and beyond, increase prospects for effective adaptation, reduce the costs and challenges of mitigation in the longer term, and contribute to climate-resilient pathways for sustainable development.

Without additional mitigation efforts beyond those in place today, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, widespread, and irreversible impacts globally (high confidence). Mitigation involves some level of co-benefits and of risks due to adverse side-effects, but these risks do not involve the same possibility of severe, widespread, and irreversible impacts as risks from climate change, increasing the benefits from near-term mitigation efforts.

There are multiple mitigation pathways that are likely to limit warming to below 2°C [3.6°F] relative to pre-industrial levels. These pathways would require substantial emissions reductions over the next few decades and near zero emissions of CO2 and other long-lived GHGs by the end of the century. Implementing such reductions poses substantial technological, economic, social, and institutional challenges, which increase with delays in additional mitigation and if key technologies are not available.

I encourage you to dig into the full synthesis report for more detail. You may also want some information on how climate change is affecting your local area. For that, look to the solid, accessible findings of latest US National Climate Assessment, released this past spring.

Since the IPCC turned from review of new publications to synthesis last year, scientists at the Global Carbon Project reported that global emissions of carbon dioxide from fossil fuel burning and cement production reached record levels in 2013, rising 2.3% above the previous year and are projected to rise another 2.5% by the end of 2014. Emissions have now risen more than 60% since 1988, the year that the IPCC was formed and the scientific community’s concerns about climate change first received widespread public attention.

I hope this helps. You don’t have to be a scientist. Really. You just have to listen to them. And then draw upon their advice, your commitment to evidence-based decision-making, and your obligation to current constituents and future generations by getting to work ensuring that our nation is a leader in setting strong sensible climate policies.

I know you can do this.


© 2021 Union of Concerned Scientists

Peter Frumhoff

Peter Frumhoff is a global change ecologist and serves as chief scientist for the UCS climate campaign. Dr. Frumhoff is an internationally-recognized expert on climate change impacts, climate science and policy, tropical forest conservation and management, and biological diversity. He holds a Ph.D. in Ecology.

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