A growing body of scientific information shows that the Earth is warming, mainly because humans have released greenhouse gases into the atmosphere. Those gases trap some of the Sun’s energy and warm the atmosphere, ocean, and land. The increase in temperature is affecting many aspects of the climate system, including melting of ice sheets and ocean acidification.
The most important factor driving climate change is the concentration of carbon dioxide in the air. When fossil fuels are burned, CO2 is released into the atmosphere. The air’s temperature rises as a result, and the ocean’s temperature rises even faster. In addition, natural processes, like permafrost melt and the loss of Amazon rainforest, can add to or subtract from global warming by increasing or decreasing CO2 levels.
While the current climate system has changed throughout history, human activities are contributing to the fastest rate of change in recent millennia. Climate scientists agree that keeping temperatures below 1.5° Celsius (2.7° Fahrenheit) would reduce the severity of impacts and keep the planet habitable.
Achieving that goal will require a swift and far-reaching transition to low-carbon, clean energy for all sectors of the economy. In some scenarios, the resulting changes in global net human-caused emissions of CO2 will be close to zero by 2050. However, uncertainties about future societal factors and physical processes lead to large variations in projections of CO2 emissions under implemented policies. This is why it’s important to understand the risks of climate change as early as possible, and why everyone needs a plan for responding to its impacts.