Which Country Does Adversely Affect The World’s Climate Mostly?

The past century has seen a 0.8°C (1.4°F) increase in global average temperature, and according to the Intergovernmental Panel on Climate Change (IPCC), the amazing source of this growth has been emissions of greenhouse gases and other pollutants from human activities. Scientists have also observed that many of Earth’s glaciers, ecosystems and other systems are already being impacted by rising regional temperatures and altered rainfall amounts and patterns.

What remains unclear is precise what fraction of the observed changes in these climate-sensitive systems can confidently be attributed to human-related influences, rather than mere natural regional fluctuations in climate. So Gerrit Hansen of the Potsdam Institute for Climate Impact Research in Germany and Dáithí Stone of Lawrence Berkeley National Laboratory (Berkeley Lab) developed and applied a novel methodology for answering this challenging question. Their work was published in Nature Climate Change on December 21, 2015.

Their PC modeling-based study concentrated on various particular regional impacts around the world identified in the last IPCC report (such as vanishing glaciers and snow ice in Europe, changes in terrestrial ecosystems in Asia, wildfires in the state of Alaska, etc.).  The IPCC report listed over 100 such impacts of various kinds in different regions across the globe. The Hansen-Stone study focused on the regional climate trends relevant to these effects over the 40-year period 1971-2010.

Using a sophisticated algorithm, the study necessarily required satisfaction of three distinct types of tests.  First, the algorithm assessed the adequacy of the available climate data—the so-called observational record—related to the particular regional impact over the 40-year period.  Was the data sufficient to provide a basis for understanding what had been taking place?  Next, the algorithm determined whether the climate models the researchers used provided sufficient resolution or detail concerning regional climate so as to be considered an appropriate source of knowledge.  Finally, the researchers examined collections of model simulations with and without human emissions factored in to understand to what degree human emissions were responsible for a given impact, by comparing these simulations against observed trends.

Linda Vu, Berkeley Lab Computing Sciences