| Summary: | We consider information from many sciences bearing on the causes and consequences of climate change, focusing on lessons from past mass extinctions of life on Earth. The increasing atmospheric levels of the main greenhouse gases are now established, as is their source in human activity. World-wide temperatures are rising on a high variance stochastic trend. Evidence from the past 500 million years provides a major warning: climate change is the main culprit in previous mass extinctions, with several different triggers - humanity is the latest trigger. The different approaches and sources of evidence across so many disciplines make a compelling case. Economic analysis offers a number of ideas, but the key problem is that distributions can shift, making action to avoid possible future shifts urgent. Adaptation ceases to be meaningful if food, water and land resources become inadequate, whereas the first migration steps are not costly and should stimulate innovation, creating opportunities as new technologies develop.
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