Climate change is significant change in climate patterns over time. Climate is the set of weather patterns that occurs in an area over a long time, years, decades, or centuries. It is distinct from weather, which is the set of conditions of temperature, precipitation, humidity, cloud cover, and wind speed at a given moment in a given place. Weather is short term. Climate is long term.
Climate change occurs when the prevailing weather patterns change significantly and do not return to their previous pattern. For example, a region might have heavy rains every April and May for 150 years. If those heavy rains move to June and July and stay there for the next 30 years without returning to April and May, the climate is said to have changed.
Climate has changed throughout Earth's history. Regions have changed from hot to cold and from wet to dry. Forests once grew on Antarctica, but that climate changed long ago, and now Antarctica is covered with ice. Ice ages have periodically dropped surface temperatures Page 121 | Top of Articlefor periods of thousands or millions of years. About 20,000 years ago, most of North America was covered with glaciers.
Sidebar: HideWORDS TO KNOW
- continental drift:
- The slow movement of Earth's landmasses around its crust over millions of years.
- Substances discharged into the air as a by-product of burning, such as the exhaust from a car engine.
- No longer alive on Earth.
- fossil fuel:
- Any fuel formed by the decomposition of dead organisms over several million years, including coal, petroleum, and natural gas.
- A slowly flowing mass of ice created by years of snowfall and cold temperatures.
- greenhouse gas:
- A gas that traps heat in the atmosphere; the main greenhouse gases are water vapor, carbon dioxide, methane, and ozone.
- ice age:
- A period of low temperatures that lasts for thousands or millions of years, resulting in the formation of polar ice sheets and glaciers.
- ice cap:
- A mass of glacial ice that covers less than 19,000 square miles (50,000 square kilometers) of a landmass.
- mass extinction:
- Disappearance of a large percentage of Earth's species in a short time.
- The process by which plants and algae use the Sun's energy to convert carbon dioxide and water into sugars.
- The massive explosion of a star at the end of its life, creating a burst of bright light.
- The set of conditions of temperature, humidity, cloud cover, and wind speed at a given time.
Organisms such as plants and animals are usually adapted to the climate in which they evolved and cannot live in very different conditions. Plants that are adapted to cold climates cannot survive if temperatures get hotter. Frogs that reproduce in ponds cannot survive if those ponds dry up. Climate change in the past has caused mass extinctions, in which large percentages of all the world's plants and animals died. Climate change has also influenced human settlement patterns and agricultural practices.
Why climates change
Climate is the product of many factors, including ocean currents, solar intensity, volcanoes, continental drift (the movement of Earth's landmasses around the planet), and wind patterns. Living organisms themselves affect climate. Plants and algae living on the land and in the ocean constantly cycle carbon and water, changing the composition of the atmosphere by adding oxygen and water vapor to it and removing carbon Page 122 | Top of Articledioxide during photosynthesis, the process by which plants use the Sun's energy to convert carbon dioxide and water into sugars. Carbon dioxide is a greenhouse gas, which holds the Sun's heat close to Earth's surface and make the planet hotter. Removing carbon dioxide from the atmosphere makes it cooler.
Plants have played a significant role in several of Earth's major climate changes. Earth's climate has changed many times over the planet's 4.54 billion year history. It started out very hot. It seems to have been completely frozen over around 2.3 billion years ago; scientists believe this was the result of the first photosynthetic organisms removing vast amounts of carbon dioxide from the atmosphere, which allowed global temperatures to drop. Earth was frozen over again about 650 million years ago, and again about 360 million years ago, both of these also possibly caused by plants changing atmospheric composition.
Plants take greenhouse gases out of the air. Volcanoes and earthquakes can put it back in. Volcanic eruptions emit large amounts of carbon dioxide from Earth's interior. Cracks in the ocean bottom can emit methane, an even stronger greenhouse gas. Massive volcanic eruptions seem to have contributed to mass extinctions 252 million years ago and again 232 million years ago. The 1883 eruption of the volcano Krakatoa in Indonesia darkened skies around the world and caused global temperatures to drop for five years.
The arrangement of landmasses affects climate. Large continents with a low ratio of coastline to interior have harsher and drier climates than smaller landmasses with ample ocean exposure. The color and texture of surfaces affects climate; large ice caps, for example, contribute to increased ice formation because they reflect the Sun's rays away from the surface.
Even objects from outer space can change Earth's climate. Scientists have suggested that events in distant stars such as supernovas and gammaray bursts might have caused some mass extinctions. An asteroid crashing into Earth 66 million years ago kicked up so much dust that plants could not get enough solar energy to perform photosynthesis. Plants and animals died, including the dinosaurs. Fires might have raged, burning off oxygen in the atmosphere and increasing carbon dioxide levels, creating a greenhouse effect that killed still more organisms.
Human causes of climate change
Clearly many factors can change climate, including the actions of living organisms. Today human activities are causing rapid climate change. Global Page 123 | Top of Articletemperatures have increased steadily since the 1950s; the decade between 2002 and 2012 was the warmest decade ever recorded. International and U.S. agencies and many different scientific associations have agreed that Earth's climate has been seriously changed by human activities. There is clear consensus on this in the scientific community. Scientists may debate the details, but there is no question that human activities are changing atmospheric composition and the nature of Earth's surface.
Over the past century, humans have added vast amounts of carbon to the atmosphere. This is the result of burning fossil fuels. Fossil fuels, including coal, petroleum, and natural gas, are underground deposits of carbon that have been buried for millions of years. Most of them formed during the Carboniferous period, 359 million to 299 million years ago. During this period, Earth was covered with forests. These plants removed so much carbon dioxide from the air and emitted so much oxygen in the process that Earth's oxygen levels were actually much higher than they are now. When these plants died, they were eventually buried deep underground, and all of the carbon they contained was slowly converted into fossil fuels. All of that carbon has been hidden in the ground for about 300 million years.
Removing fossil fuels from the ground and burning them releases several million years' worth of carbon dioxide into the atmosphere. This raises the level of carbon dioxide in the atmosphere. The Mauna Loa Observatory in Hawaii has been tracking carbon dioxide levels since 1960, and those levels have risen at a steady rate every year. In 2013, they went over 400 parts per million, the highest level ever recorded and a level many scientists consider dangerous.
Predictably, this increase in carbon dioxide has been accompanied by generally rising temperatures worldwide and other signs ofwarming, such as decreased ice in the Arctic and melting mountain glaciers. Sea levels have started to rise as that melting ice enters oceans.
Implications of climate change
The effects of climate change are visible and well documented. Plants and animals have moved to different territories or gone extinct in their current ranges because they cannot live in the new climate. Humans have migrated as well, as their homelands are degraded by desertification or are impacted by rising sea levels. Increased temperatures are a particularly big problem and are killing people already.
The Intergovernmental Panel on Climate Change (IPCC) has been studying climate change for years and has issued several reports and predictions. In the future, sea levels will likely rise, and weather will become more extreme, with longer, hotter heat waves, more floods, increasing drought, and strong storms. These trends will continue for decades because human emissions continue. Even if humans immediately end all carbon emissions, which would mean no more automobiles fueled by gasoline and no more electrical power produced by burning coal or other fossil fuels, temperatures would increase for years to come due to the greenhouse gases already in the atmosphere. This is likely to cause various crises: water shortages, lowered agricultural yields, and loss of biodiversity.
The World Health Organization estimated in 2014 that the health impacts of climate change already cause about 150,000 deaths per year, and this will rise to about 250,000 deaths per year by 2030. Those deaths will be due to heat stress, malnutrition (from failed crops), diarrhea (from unsanitary water), and malaria. Increased levels of pollen and ozone will increase respiratory ailments. Elderly people will be endangered by hot summers, such as the 2003 summer heat wave that killed 70,000 in Europe. Developing nations will be hit the hardest.