Climate change is the warming of Earth’s atmosphere and surface caused by human activities. This warming affects our health and well-being, food security, water resources, ecosystems, and economies around the world. Climate change is already having serious impacts and will continue to do so unless we act now.
The underlying cause of climate change is a large buildup of heat-trapping greenhouse gases in the atmosphere. These gases absorb and re-radiate energy from the Sun, warm the lower atmosphere, and slow heat loss to space. They include carbon dioxide, methane, nitrous oxide, and several human-made gases that contain fluorine or chlorine. These gases are released into the atmosphere when fossil fuels (oil, natural gas, coal) are burned. Other factors affecting climate over the long term include volcanic eruptions, shifts in Earth’s orbit, and plate tectonics.
Although some of the recent warming has been due to these natural phenomena, human activity is largely responsible for recent climate changes. In addition, some research indicates that if greenhouse gas emissions continue unabated, Earth could reach dangerously high levels of warming.
The effects of climate change vary by region and can be complex, but some are already evident. For example, higher summer temperatures are associated with increased deaths from heat-related illnesses, especially in older adults and young children. Climate change also increases the amount of ground-level ozone, which can damage lungs and other respiratory systems. It causes air pollution to worsen in places that lose trees, and it creates conditions that can lead to wildfires, which produce particulate matter that further aggravates respiratory and cardiovascular diseases.