Enormous amount of solar radiation reaches the Earth through the atmosphere in the form of light that we can see and others we can’t see, including UV and IR. About 30% of this radiation is immediately reflected back out to space by cloud, ice, snow, sand and other reflective surfaces. The remaining 70% is absorbed by the oceans, the land and the atmosphere of the Earth.
But these elements can absorb only so much and the heated energy is released back to the atmosphere and finally into space. This way, nature establishes an equilibrium between incoming and outgoing radiation, with an average temperature of 15C. Otherwise, no life can exist on the Earth, as it would be as cold as the Moon that has no atmosphere with a temperature of about minus 153C, or as blazing hot as Venus with a dense atmosphere and an average temperature of about 46C.
The IPCC’s Fourth Assessment Report (2007) discusses the greenhouse effect. To balance the absorbed incoming solar energy the Earth must radiate the same amount of energy back to space. The Sun is extremely hot and has a lot of energy to give off, so it gives off shortwave radiation in the form of UV rays and visible light (the colours of the rainbow), because short wave radiation contains a higher amount of energy. The Earth is much cooler, but still emits radiation with much longer wavelengths, primarily in the IR form, because long wave radiation contains a smaller amount of energy.
The Earth’s ‘budget’ of solar radiation is as follows:
Absorbed by atmosphere 17.5
Scattered to the Earth from blue sky 10.5
Scattered to the Earth from clouds 14.5
Radiation going directly to the Earth’s surface 22.5
The primary greenhouse gases in the atmosphere are water vapour, carbon dioxide, nitrous oxide, methane and ozone. These greenhouse gases greatly affect the temperature of the Earth. Without them the Earth’s surface would average about 33 °C colder than the present average of 14C.
The IPCC in its Fourth Assessment Report, 2007, on climate change asserted that warming of the climate system is unequivocal and most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.
What is climate change
Climate change means any significant change in climate, such as temperature or rainfall over a 30 year period or more. If the climate is changing it means the 30 year average temperature or rainfall or number of sunny days is changing. A meteorological definition is a change in the statistical distribution of weather patterns when that change lasts for an extended period of time (i.e. decades to millions of years).
In the past century this planet had warmed up by an average of nearly 1C. This is not much in anybody’s eyes but it is creating havoc for people and wildlife. Climate change does not mean we will all just have warmer weather in future. As the Earth heats, climate patterns change but it is erratic and unpredictable across the globe. It will be extremely dry in some parts of the planet, while some places may be drier.
The climate of the Earth has been pretty stable at about 14C, after the end of the Ice Age about 11,500 years ago. But from-mid-20th century and onwards its temperature has been rising. This climate change is attributed largely to the increased levels of atmospheric carbon dioxide produced by the use of fossil fuels, and methane gas.
Scientific research shows that the climate i.e. the average temperature of the Earth’s surface has risen by 0.89C from 1901 to 2012 and there have been changes in the patterns of precipitation (water in any form falling to the Earth from the sky). Further, it is shown that the rate of temperature rise since the beginning of the Industrial Revolution is extremely high.
Scientists have noted rising sea levels since 1900 by about 19 centimetres globally on average. Glaciers are melting all over the world, as in the Himalayas, the Alps, the Rockies, the Andes, Africa and Alaska, and the rate of shrinkage of ice sheets has increased in recent decades.
The Greenland and Antarctic ice sheets, which between them store the majority of the world’s fresh water, are also shrinking and the rate is accelerating. Arctic sea ice has been known to be declining since the late 1970s. It is being reduced by about 4% – an area about the size of the island of Madagascar per decade.
Climate change is not new. Our Earth has gone through a series of warm and cold periods. Over the last 100 years we are told that its average surface temperature had gradually increased by about 0.8C. This is human enforced warming due to greenhouse effect.
What affects climate change
The climate of the Earth is affected by a number of factors – natural and man-made – which are called “forcings”, because they “drive” or “force” the climate system (the oceans, land surface, cryosphere (frozen water part), biosphere (zone of life on Earth), and the atmosphere. Changes in these forcings, such as in the amount of greenhouse gases produced, cloud particles, and in the reflectivity of the Earth’s surface, will cause imbalance in the climate. A positive climate forcing will tend to cause warming, and a negative forcing a cooling.
The most important forcings during the last millennium were the solar energy output, volcanic eruptions, and increased concentration of greenhouse gases in the atmosphere.
There are many natural causes that can affect the climate system, such as changes in solar radiation, the Earth’s rotation in its oval orbit around the Sun, and volcanic eruptions that release huge amounts of gas. Though most of this gas is removed within days to weeks, some gas like sulphur dioxide can cause global cooling, while volcanic carbon dioxide has the potential to promote global warming.
Solar radiation increases every 11-years’ cycle, known as “sunspot” cycles. Though it contributes to climate change, its intensity has been relatively constant through the last 2,000 years. Changes in solar brightness are considered to be too weak to explain recent climate changes. Changes in the reflectivity of the Earth’s surface, such as by melting of sea ice or extensive cloud cover has some impact on climate change though regionally.
Man-made causes include:
(1) Increased output of greenhouse gases
(2) Cutting down forests and breeding cattle
The increased solar energy, though responsible for the Earth’s warming till the early 20th century is now not the main cause of climate change in the global warming trend. It is due to a vast increase in the greenhouse gas production.
The strongest greenhouse effect (95%) of greenhouse gases is due to an increase in the concentration of water vapour in the atmosphere that increases the temperature as it traps heat. But water vapour does not by itself increase temperature. It amplifies already occurring warming due to additional carbon dioxide from factories and airplanes that also traps heat. And as the atmosphere warms up, the amount of water it holds increases, which further adds to the warming effect.
Modern nations cut down vast areas of forest that naturally trap carbon dioxide. As a result, the extra carbon dioxide (that stays for 100 years) in the atmosphere will absorb and emit more of the
Earth’s ongoing radiation. That will further warm up our climate.
In recent times, transformations in land use and land cover, such as deforestation, reforestation and desertification, now occurring practically in one quarter of the total land surface of the world, and urbanisation often contribute changes in climate regionally, but is small when averaged over the entire globe.
Industrialised nations are breeding vast numbers of livestock – 1.5 billion cows and billions of grazing animals. Cows produce methane gas (23 times more powerful than carbon dioxide) through belching and to a lesser extent from flatulence. Scientists are creating a pill that will convert methane into glucose in a cow’s stomach.
How does climate change produce extreme global weather
We know that climate disruption does cause a variety of extreme weather conditions and there have always been extreme weather events. But they are now occurring with increasing frequency in association with global average temperature rise, which is one of the most-cited indicators of global climate change.
This large-scale pattern of global climate change due to human influence is a significant feature present in nearly all of the studies conducted by the world’s climate modelling groups for the Fourth Assessment of the IPCC, and is also evident in observed 20th century precipitation trends.
Other scientific studies also find that since the 1960s many countries in the world are experiencing warmer climate accompanied by a reduction in the frequency of frosts, an increase in the number of heat waves and coastal flooding in many parts of the world. There is a rise in extreme precipitation events in some regions and increasingly severe droughts in others – detected by ‘Attribution Studies’ focussing on changes in extreme global events.
The writer is based in the UK