Climate change refers to a global pattern of changing weather conditions, including increasing air and ocean temperatures, long-term reductions in snow and ice cover and changes in rainfall patterns. These are the result of extra heat energy circulating through Earth’s system, mainly from human activities such as burning fossil fuels, deforestation and agricultural practices. These activities increase the amount of “heat-trapping” greenhouse gases in the atmosphere.
The Sun provides the energy that drives Earth’s climate, but the planet also reflects and absorbs some of its incoming solar radiation, and re-radiates some back into space. The concentration of carbon dioxide in the atmosphere — which is the main greenhouse gas — has been rising steadily since the late 1800s, reaching levels not seen in millions of years.
Scientists have found that the fingerprint of this increased CO2 is much closer to that of climate change induced by humans than to that resulting from fluctuations in the Sun alone. This difference is clear in observations and long-term climate records.
A warming world is affecting every part of the planet. For example, hotter weather brings more hot days and heat waves that increase the risk of high-temperature related illnesses such as heart disease and stroke. Warmer and wetter climates also favor insect-borne diseases like Lyme disease, West Nile virus and dengue fever. And as ice sheets melt and sea levels rise, they threaten low-lying areas including island nations and major cities like New York City and Mumbai in India.
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