What is Climate Change?
The science of climate change
There is a vast body of research undertaken by scientists over many years, and a key message from the recent IPCC report (5th Assessment) is that there is no longer uncertainty that global climate change is happening:
- The last decade showed the highest global average surface temperatures since records began, about 0.8°C above pre-industrial levels.
- Global sea level has risen by around 20cm with significant contributions now coming from the melting ice sheets over Greenland and Antarctica.
- Sea ice is also decreasing.
Human activity is playing a key role. The greenhouse gas effect, whereby CO2 and other gases warm the atmosphere, has been understood for over a hundred years. We have been burning increasing amounts of fossil fuels since the industrial revolution; and as a result CO2 concentrations in the atmosphere have broken out of the natural cycle seen over the last million years. There is a high degree of confidence that human emissions have caused most of the observed warming since the mid-20th Century.
If we make no efforts to cut global use of fossil fuels, global warming is likely to reach between 2-7°C this century with further warming beyond. This will have significant consequences for human welfare and ecological systems.
How are humans influencing this?
Human activities, such as burning fossil fuels and deforestation, release greenhouse gases (GHG) that would otherwise be contained in natural stores e.g. soils, trees and coal, changing the natural balance of our atmosphere and breaking out of the natural cycle seen over the past millions years.
Greenhouse gases, most notably carbon dioxide, methane and water vapour, are important in keeping our planet naturally warm by trapping heat from the sun in our atmosphere; this is known as the Greenhouse Effect. Too much of these gases in our atmosphere however trap too much heat, causing the planet to get increasingly warmer and resulting in climate change.
The IPPC advises, with a high level of confidence, that human emissions have caused most of the observed warming since the mid-20th century. It also states that continued emissions will cause further warming and changes in all components of the climate system.
Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions if we are to avoid ‘dangerous’ climate change.
For an interactive demonstration of how climate has changed, and how continued GHG emissions can change climate further, visit the Global Carbon Atlas website.