Climate change refers to a significant increase in Earth’s average temperature over the past few decades. It is the result of human activities, primarily fossil fuel use and land-use changes.
Carbon dioxide concentrations are rising mainly due to the burning of fossil fuels. Plants pulled the carbon out of the atmosphere through photosynthesis over millions of years, but we are returning it to the atmosphere in just a few hundred. When CO2 levels are high, the atmosphere traps more heat and warms the planet.
The rate at which the world warms in the future depends on many factors. Some of the key variables are uncertainty about future emissions and feedback processes that dampen or amplify the initial warming effect. In addition, there are unpredictable natural influences on climate that cannot be controlled by humans.
Almost all of the global warming observed over the last century can be attributed to human activities. However, some of the warming can also be attributed to other factors like cyclical ocean patterns such as El Nino and La Nina, volcanic activity, and changes in sunlight reaching Earth.
Even without these other factors, a doubling of carbon dioxide concentrations would lead to a 0.6 degC increase in Earth’s average temperature. This increase in global temperature is a significant contributor to many negative impacts on the world.
The most obvious impacts are on water resources and species. Warmer temperatures and changed precipitation patterns stress ecosystems. Some plants are growing faster and changing their geographic range as they adapt to new conditions, but some species are not able to keep up and are being lost. Invasive or nuisance species, such as lionfish and ticks, are spreading to more places as the climate changes, adding to the stress on local ecosystems.
Other climate change impacts include the spread of diseases. Mosquitoes and other insects that transmit infectious diseases can only thrive in certain environments, so the spread of such illnesses as malaria, dengue fever and chikungunya will likely accelerate as the climate continues to warm.
Climate change is also impacting humans, with higher risk of climate-related events and lower adaptive capacity to respond. This is especially true for people living in vulnerable regions, such as island nations and developing countries. A recent study found that highly vulnerable regions experienced 15 times as many deaths from floods, droughts and storms compared to those in low vulnerability.