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Are human activities or natural variations in climate responsible for the climate changes observed today?

Question: Are human activities or natural variations in climate responsible for the climate changes observed today?

Response: 

The Earth does go through natural cycles of warming and cooling, caused by factors such as changes in the sun or volcanic activity. This has been closely examined, and the warming we have seen in the past 50 years cannot be explained by natural factors alone. 1 This figure illustrates one piece of evidence that shows that recent global warming is primarily a result of greenhouse gas emissions from human activities.

ยป Learn more about the causes of climate change.

 

Models that account only for the effects of natural processes are not able to explain the warming over the past century. Models that also account for the greenhouse gases emitted by humans are able to explain this warming. View enlarged image

This figure shows the observed average global temperatures from 1900 to 2000 (black line) along with the temperature ranges predicted by climate models. The blue band shows the expected temperature range based on climate models that account only for natural forces. The pink band represents the temperature range predicted by climate models that also include emissions of greenhouse gases from human activities. The recent increase in average global temperatures aligns with the predicted temperatures from the model that includes the greenhouse gas emission.
Source: USGRCP 2009

 

 

1. USGCRP (2009). Global Climate Change Impacts in the United States . Thomas R. Karl, Jerry M. Melillo, and Thomas C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

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Topic Information
  • Topic #: 23002-33346
  • Date Created: 4/16/2012
  • Last Modified Since: 6/5/2012
  • Viewed: 3346

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