The Effects of Human Activity on the Climate of Earth

The climate of Earth has changed over time, and human activity is a major driver. Fossil fuel burning adds heat-trapping greenhouse gases to the atmosphere, which warms it. Many other human activities also contribute to warming. These include cutting down forests (deforestation), growing livestock and using fertilizers containing nitrogen and fluorinated gases, which have a greater warming effect than carbon dioxide, but only for a short time. Natural factors, like volcanic eruptions and shifts in the Earth’s orbit, can also change the climate.

Almost all parts of the world are warmer now than in the past. This change is happening faster than scientists previously expected, and it will have wide-ranging effects. The polar ice sheets are melting, and sea level rise is accelerating. The global average temperature is expected to increase by about 2.7 degrees Fahrenheit over the next century.

Temperature extremes are becoming more frequent and severe. Floods, droughts and wildfires are causing widespread damage. Coastal ecosystems and low-lying areas are particularly vulnerable, and people who live in these regions are often the first to experience the negative impacts. In addition, human health is increasingly at risk due to rising temperatures, heat stress and decreased air quality.

Scientists have strong evidence that humans are responsible for the warming of the atmosphere, ocean and land. The Fifth Assessment Report by the Intergovernmental Panel on Climate Change, a group of more than 500 independent scientists from around the world who worked under United Nations auspices, is unequivocal: “The evidence for human influence on the climate system is now very clear. The changes seen over the last few decades are unprecedented over many centuries to thousands of years.”

The Climate Science Special Report of the U.S. National Climate Assessment, a scientific report required by Congress, is the most comprehensive climate change assessment produced to date. It includes an evaluation of current and projected impacts, a range of climate change mitigation options and an analysis of potential risks to people and natural resources.

This report builds upon the conclusions of the Third U.S. National Climate Assessment, published in 2014. Since then, stronger evidence has emerged that the warming caused by human emissions of greenhouse gases is continuing. Scientists have also been able to better pinpoint the human influences on individual climate and weather events.

The most serious threats from climate change are posed to the world’s poorest people. Those who contributed the least to its causes, and are the most vulnerable to its impacts – including the elderly, children, low-income households, and the most marginalized communities — face the greatest challenges in adapting to changing conditions. They are least able to afford the most costly solutions. In the long run, they will be unable to cope with increasing climate risks. The most urgent action is needed to slow down the pace of warming and reduce the amount of carbon we release into the atmosphere. This will require a profound transformation of energy, transportation, agriculture, urban design and other aspects of the economy.

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