What is Climate Change?

Dry ground

Climate change is a change in weather patterns caused by changes in the atmosphere. This includes changes to levels of rain and heat as well as air currents and humidity, which can be measured over geological time. The weather is affected by the oceans, land surfaces and ice sheets, which together form the ‘climate system’. By measuring the state of the climate system, it is possible to calculate climate change. Today, the global average temperature is about 15 Celsius, though geological evidence suggests it has been much higher and lower in the past.

Climate change is when there is a change in the climate system that has continued for at least three decades, measured through averages, variability and extremes. These changes may be caused by natural processes, such as solar energy, volcanic eruptions as well as natural changes in greenhouse gas (GHG) concentrations. It is also affected by human influences. The most impact since the beginning of the Industrial Revolution in the mid-eighteenth century include the burning of fossil fuels and conversion of land from woodlands and jungles to agriculture.

Predicting climate change

Forecasting what the weather will do from one season to the next is particularly unreliable because it is looking at a small sample over a short period of time. In contrast, climate change can be measured when the causes are known to be long-term, such as human activities which have predictable effects on the future atmospheric composition, and in turn a predictable effect on climate.

Factors that determine climate

The energy in the climate system is influenced in many ways.

Solar energy

Solar energy drives the weather. Over millions of years, the solar intensity has influenced the climate, being responsible for example, for the ice ages. The energy rate from the sun varies daily, and the level of energy the Sun is dependent on the orbital relationship between the two planets. Some of this sunlight is reflected directly back to space by the atmosphere, clouds, and the Earth’s different surfaces. Aerosols, tiny particles in the atmosphere, (some of which are caused by human activities) can also increase the amount of sunlight reflected back. Yet the growing rate of solar heating over the last 50 years, cannot be blamed on solar energy.

Heat radiation

In the process of interacting with the entire climate system, the solar energy absorbed by Earth is returned to space as heat radiation, which determines the climate. The two the main gases in the atmosphere, nitrogen and oxygen, are unaffected by infrared radiation, but greenhouse gases absorb this radiation coming up from the Earth’s surface and they re-radiate it in all directions, including back down to earth, which causes the ‘greenhouse effect’.

The Greenhouse Effect

Some of the energy from the Sun trapped in the Earth's atmosphere heats the lower atmosphere and the surface of the planet. Without this natural greenhouse effect, the Earth’s surface would be about 33 degrees cooler than it is now. Identified more than 100 years ago, scientists have estimated that the greenhouse effect has kept Earth habitable.

Industry and agriculture are the cause of the increasing greenhouse effect, also known as global warming or climate change, according to researches. They add more gases, most significantly water vapour, carbon dioxide (CO2) and methane, which trap energy like a blanket, which increases the Earth’s temperature.

Water vapour

Water vapour is the most important of all the greenhouse gases in that it makes the biggest contribution to warming, but the concentrations are relatively stable, and it stays in the atmosphere for just a few days.

Carbon dioxide

Carbon dioxide (CO2) stays in the atmosphere for a long time and is the largest contributor of all the greenhouse gases. Currently, there is too much CO2 for the Earth to manage. This is due to the burning of fossil fuels. Carbon fuels such as coal, oil or gas are used to generate steam that has been driving large turbines and producing a reliable supply of electricity for decades. However, a by-product of this burning is carbon dioxide, the main cause of human-induced climate change. The levels of CO2 are also rising as acres of carbon-absorbing forests are levelled.


Methane is caused by the decomposition of plant matter and is released from landfills, swamps and rice paddies. Cattle also release methane. Although methane emissions are lower than carbon dioxide emissions, it is considered a major greenhouse gas because each methane molecule has 25 times the global warming potential of a carbon dioxide molecule, but the levels are still small in comparison to CO2.

Nitrous oxide

Nitrous oxide is released from bacteria in the soil. Modern agricultural practices including soil cultivation, livestock waste management, and the use of nitrogen-rich fertilisers all make a significant contribution to nitrous oxide emissions. A single nitrous oxide molecule has 298 times the global warming potential of a carbon dioxide molecule, but the levels are still small in comparison to CO2.

Natural and human-induced causes of climate change

The global climate naturally varies over timescales from decades to thousands of years. The concern with the current period of warming is that it is happening faster than at any other time in the past. In addition, the natural variations that could be expected are being surpassed by the speed of human-induced warming which has a potentially serious impact on the stability of the planet's climate.

Intergovernmental Panel on Climate Change Report

In October 2018, the Intergovernmental Panel on Climate Change published a report on impacts and possible methods of keeping temperatures from warming by more than 1.5 degrees Celsius above pre-industrial times. If the temperature goes above this level, the consequences for the planet and its inhabitants are dire. Yet whilst the report is alarming, it is also hopeful since the authors believe it is possible to limit warming to 1.5 degrees Celsius. To do this requires huge changes to life on Earth. To not do anything at all will also require huge changes to life on Earth.