Climate Change and Its Effects
The term climate refers to the general weather conditions of a place over many years. In the United States, for example, Maine’s climate is cold and snowy in winter while South Florida’s is tropical year-round. Climate change is a significant variation of average weather conditions—say, conditions becoming warmer, wetter, or drier—over several decades or more. It’s that longer-term trend that differentiates climate change from natural weather variability. And while “climate change” and “global warming” are often used interchangeably, global warming—the recent rise in the global average temperature near the earth’s surface—is just one aspect of climate change.
Greenhouse gases
The greenhouse gas with the greatest impact on warming is water vapour. But it remains in the atmosphere for only a few days. Carbon dioxide (CO2), however, persists for much longer. It would take hundreds of years for a return to pre-industrial levels and only so much can be soaked up by natural reservoirs such as the oceans. Most man-made emissions of CO2 come from burning fossil fuels. When carbon-absorbing forests are cut down and left to rot, or burned, that stored carbon is released, contributing to global warming.
Since the Industrial Revolution began in about 1750, CO2 levels have risen more than 30%. The concentration of CO2 in the atmosphere is higher than at any time in at least 800,000 years. Other greenhouse gases such as methane and nitrous oxide are also released through human activities but they are less abundant than carbon dioxide.
The world is about one degree Celsius warmer than before widespread industrialisation, the World Meteorological Organization (WMO) says. The 20 warmest years on record all occurred in the past 22 years, with 2015-18 making up the top four. Across the globe, the average sea level increased by 3.6mm per year between 2005 and 2015. 
Most of this change was because water increases in volume as it heats up.
However, melting ice is now thought to be the main reason for rising sea levels. Most glaciers in temperate regions of the world are retreating. And satellite records show a dramatic decline in Arctic sea-ice since 1979. The Greenland Ice Sheet has experienced record melting in recent years. Satellite data also shows the West Antarctic Ice Sheet is losing mass. A recent study indicated East Antarctica may also have started to lose mass. The effects of a changing climate can also be seen in vegetation and land animals. These include earlier flowering and fruiting times for plants and changes in the territories of animals.
Effects of climate change
Increase in average temperatures and temperature extremes
One of the most immediate and obvious effects of global warming is the increase in temperatures around the world. The average global temperature has increased by about 1.4 degrees Fahrenheit (0.8 degrees Celsius) over the past 100 years, according to the National Oceanic and Atmospheric Administration.
Extreme weather events
Extreme weather is another effect of global warming. While experiencing some of the hottest summers on record, much of the world has also been experiencing colder-than-normal winters.
Changes in climate can cause the polar jet stream — the boundary between the cold North Pole air and the warm equatorial air — to migrate south, bringing with it cold, Arctic air. This is why some states can have a sudden cold snap or colder-than-normal winter, even during the long-term trend of global warming.
Displacement of the people
Climate change may become the biggest driver of displaced people, according to IPCC. In 2008, 36 million people were displaced by natural disasters. At least 20 million of those people were driven from their homes by disasters related to climate change like drought and rising sea level.
Costs for society and economy
Damage to property and infrastructure and to human health imposes heavy costs on society and the economy. Between 1980 and 2011 floods affected more than 5.5 million people and caused direct economic losses of more than €90 billion. Sectors that rely strongly on certain temperatures and precipitation levels such as agriculture, forestry, energy and tourism are particularly affected.
Risks for wildlife
Climate change is happening so fast that many plants and animal species are struggling to cope. Many terrestrial, freshwater and marine species have already moved to new locations. Some plant and animal species will be at increased risk of extinction if global average temperatures continue to rise unchecked.
Health
Human health is vulnerable to climate change. The changing environment is expected to cause more heat stress, an increase in waterborne diseases, poor air quality, and diseases transmitted by insects and rodents. Extreme weather events can compound many of these health threats.
Threats to environmental habitat
Ecosystems are also affected by climate change. Habitats are being modified, the timing of events such as flowering and egg laying are shifting, and species are altering their home ranges. Changes are also occurring to the ocean. The ocean absorbs about 30% of the carbon dioxide that is released into the atmosphere from the burning of fossil fuels. As a result, the ocean is becoming more acidic, affecting marine life. Rising sea levels due to thermal expansion and melting land ice sheets and glaciers put coastal areas at greater risk of erosion and storm surge.
Food
Our food supply depends on climate and weather conditions. Although agricultural practices may be adaptable, changes like increased temperatures, water stress, diseases, and weather extremes create challenges for the farmers and ranchers who put food on our tables.
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