Last December, 195 nations agreed on a plan to limit man-made (anthropogenic) warming to below 2°C (3.6°F) by the end of the century. Every signatory recognized that humanity is altering the climate, but how many dangerous climatic events can be directly attributed to human activity? According to one comprehensive study published in Nature Climate Change, a remarkable two-thirds of those occurring between 1971 and 2010 can be.
It’s overwhelmingly accepted by the scientific community that since the start of the Industrial Revolution, humankind is causing the world to rapidly warm. With warming since the beginning of this period occurring a remarkable 47,100 times faster than the temperature change during the last naturally occurring greenhouse period, it shouldn’t come as a surprise that we are already seeing the dangerous consequences of this.
Directly connecting specific climatic patterns to man-made greenhouse gas emissions, however, is no mean feat. Climate system science is incredibly complex, and it is notoriously difficult to trace back from an event to find a definitive cause, or series of causes.
This is where computer processing comes in, and for this particular study, a novel series of algorithms were constructed. These first assessed how precise the available climate data for the chosen 40-year period actually is, in relation to the impact various phenomena had in specific regions across the globe. Secondly, the equations determined if the resolution – the fine, precise detail – of the data for each event was high enough to be able to attribute primary causes to.
Finally, cutting-edge climate change simulations were used to work out how much anthropogenic greenhouse gas emissions were responsible for these events, comparing them to both current trends and models of the world’s climate without human interference being factored in.
The confidence in attributing observed impacts to climatic trends, taking into account atmospheric and ocean surface temperatures, and precipitation. Gerrit Hansen, Potsdam Institute for Climate Impact Research.
The climatic phenomena, all occurring between 1971 and 2010, were then categorized: wildfires, glacier and permafrost shrinkage, coastal erosion, floods, droughts, forest and marine ecosystem damage destruction all made the list. In addition, weather-based impacts on human food production, health, livelihoods, and the global economy were also taken into account.
The result of each computational test, which linked the observed climate record with its impacts on world regions, were all given a numerical value denoting how confident the correlation was. Dáithí Stone, one of the coauthors of the study, said in a statement that “there are many ways we could combine the scores, but we found that it didn't matter which plausible method we used – the results all pointed to the same conclusions.”
Their analysis revealed that roughly two-thirds of the listed climate impacts related to oceanic and atmospheric warming could be confidently attributed to anthropogenic emissions. This included dramatic floods, glacier shrinkage, and damage to forested and marine ecosystems. Only regional precipitation changes could not be confidently linked to human activity.
These studies are critical for understanding the nuanced differences between an Earth that warms only 2°C (3.6°F), and one that, for example, warms 4°C (7.2°F). Not only are humans directly responsible for many dangerous climatic events, but we are beginning to know just how specifically culpable we are.