Climate Change refers to changes in Earth’s average temperature and other weather patterns that are caused by human activities. The changes are causing many effects, including melting ice sheets and sea levels rising, droughts and heat waves, and changing ecosystems. The changes are expected to become more severe over time.
Most scientists agree that climate change is happening and that humans are largely responsible for the changes. While there are a few people who still question the science, most of the world’s nations have signed international agreements to limit the amount of greenhouse gases that humans can emit.
Scientists use a wide variety of evidence to study the planet’s atmosphere and surface, from temperature records at stations and on ships starting in the 1880s to satellite observations that cover the whole planet. There’s also a massive body of data from geologic sources: bubbles trapped in ice, for example, show that atmospheric CO2 concentrations have varied on long-term scales over millions of years, depending on how much volcanic activity cooled the Earth and how much carbon got removed through natural processes. Over the past century, though, atmospheric concentrations have risen rapidly, thanks to the burning of fossil fuels.
The most important measure of how warm the planet is getting, which we can track in real time, is global annual averaged temperatures. Since the start of the 20th century, global temperatures have risen by about 2 degrees Fahrenheit. The pace of warming is faster than ever before.
In addition to a rise in average temperatures, we can expect hotter days and longer, more intense heat waves. These extreme weather events can cause a variety of problems, from damaging crops and buildings to reducing the availability of fresh water and harming wildlife.
Some species may not be able to adapt to climate change and could disappear entirely. And warmer climates will also reduce the ability of many crops to grow, leading to food shortages in some areas.
Scientists also predict that the amount of precipitation will increase in some places while decreasing in others, affecting crop yields and biodiversity. They’ve also found that ocean acidity is increasing and sea levels are rising due to thermal expansion and melting ice sheets.
Several different models formulated by scientists to chart climate patterns have been used to make predictions about future changes. The models have never been 100 percent accurate, but they have consistently shown that global averaged temperatures are rising and that humans are the main cause of these changes.
The models that the Intergovernmental Panel on Climate Change (IPCC) uses to assess how dangerous climate change will be show that, if we continue to emit greenhouse gasses at current rates, there is a high risk of crossing so-called “tipping points,” which are thresholds beyond which changes accelerate and become irreversible. The most likely tipping point is the loss of Arctic ice sheets, which will lead to more rapid sea level rise and less protection from floods and storm surges.