Climate Change is the long-term shift in temperatures and weather patterns that result from natural or human causes. Warmer temperatures have a number of impacts that affect people across the globe, from straining agricultural systems and driving wildlife habitat changes to flooding and wildfires that disrupt communities and jeopardize personal safety. These impacts, referred to as “climate change impacts”, also include heat stress that can lead to health problems such as cardiovascular disease and heat stroke, and increased susceptibility to infections from mosquitoes and other insects.
Humans cause the most change to Earth’s climate, mostly through burning fossil fuels such as coal, oil and gas. These fuels release greenhouse gases into the atmosphere, which act like a blanket wrapping around Earth and trapping the sun’s warmth. Other human activities, such as land clearing and pollution, also affect how much heat is absorbed by the atmosphere. Combined with natural factors such as solar variability and volcanic eruptions, scientists have determined that it is extremely likely that more than half of the observed warming since 1850 can be attributed to human activity.
When a warming trend is considered in the context of global trends such as unsustainable use of natural resources, increasing urbanization, social inequalities, loss and damage from extreme events and a potential pandemic, climate change poses significant risks to human well-being and sustainable development. These challenges can be addressed only by governments, civil society, the private sector and other actors working together to prioritize risk reduction and climate justice.
Scientists have known for centuries that gases in the atmosphere, such as carbon dioxide and methane, prevent a certain amount of the Sun’s heat radiation from escaping into space. Over time, these gases naturally cycle in and out of the atmosphere through volcanoes and Earth’s carbon cycle (animals breathe in oxygen and breathe out CO2 and plants absorb it). But since humans began to greatly increase their emissions, the concentration of greenhouse gases in the atmosphere has risen, causing warming.
In addition, some greenhouse gases can have a feedback effect on other factors that impact the climate system: for example, higher temperatures in polar regions melt sea ice and snow, exposing darker ocean and land surfaces to more sunlight and further warming; or warmer air masses hold more water vapour, which is another potent greenhouse gas that amplify warming and whose increase is often linked to rising temperatures themselves.
Many countries have made pledges to reduce greenhouse gas emissions in order to limit the expected global temperature rise, with a goal of reaching net zero by 2050. However, recent emissions have been higher than predicted and there is a significant risk that the world will overshoot its targets and warm even more. In fact, the current trajectory could see a temperature rise of 3.6C or more by 2100. This is more than twice the target that was set by the Paris Agreement at COP24 in December 2017. Figure 2. Land mean surface temperatures from Berkeley Earth and the modeled influence of different radiative forcings with their respective uncertainties (shaded areas) for the period from 1750 to 2100.