Is Climate Change a Natural or Human-caused Phenomenon?


Two completely different lines of evidence demonstrate that the warming of recent decades results primarily from the release of greenhouse gases, chiefly CO2, by human activities. Though present, natural drivers are too weak or are trending in the wrong direction to explain the observed climatic changes.



Fingerprint of Warming by Greenhouse Gases

First, the observed, simultaneous warming of the lower atmosphere (troposphere) and cooling of the upper layers of the atmosphere (stratosphere and higher) in recent decades is a unique ‘fingerprint’ of warming by greenhouse gases. Warming from an increase in solar intensity would warm all layers of the atmosphere simultaneously. Over the past 30 years, satellite observations show that the troposphere has been warming while the stratosphere has been cooling simultaneously (see figure).

Human Induced Trends

A more detailed, state-of-the-art attribution of various climate trends is possible using optimal fingerprinting approaches that match individual forcings (for example, greenhouse gases, solar intensity or airborne particles) to observed climate change patterns using global climate models. This technique has detected human-induced trends in a wide variety of climate variables including land surface warming, vertical warming of the oceans, loss of Arctic sea ice cover, and changes in precipitation patterns at different latitudes on the Earth. Observations of global land and ocean surface warming and warming of all continents except Antarctica show that no combination of forcings that excludes manmade greenhouse gases can explain the warming trend of the past half-century (see figure).

Source: Center for Climate and Energy Solutions


This article is part of our educational series on Climate Change. See related articles below. 

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