Climate Change - The Basics
Why is a stable climate important?
The chemistry of the body can only function under certain conditions e.g. enough oxygen circulating in the bloodstream, the cells of the body at a certain temperature. The body will always try to maintain an internal environment that allows the cells to function at their optimum. The same applies to other animals and the vegetation they live on.
A reason that homo sapiens has survived over thousands of years is that the planet’s conditions have been just right. Important factors in this have been the stability of temperature and climate.
What keeps the planet’s temperature and climate stable?
The temperature of the earth is determined by the balance between the energy the earth gains from the sun and the energy it then loses out into space.
The Greenhouse Effect : The energy arriving from the sun can pass through the atmosphere almost unchanged and it warms the earth. The heat from the earth leaves its surface as infrared radiation. This is partly absorbed by gases in the atmosphere. Some of this captured energy is then re-emitted back to the earth's surface.
This natural greenhouse effect tends to warm the lower atmosphere (troposphere) and keeps the surface of the earth around 33°C warmer than it would be in the absence of greenhouse gases.
Anything that alters this balance can affect climate.
What are the gases in the atmosphere that absorb the heat from the earth?
The main naturally occurring greenhouse gas is water vapour, but the following are also important :
- carbon dioxide (CO2),
- ozone (O3),
- methane (CH4)
- nitrous oxide (N2O).
Which is the most important of these gases for climate change?
Carbon dioxide is the most important and it is the main man-made contributor to global warming. It makes up around 80% of the UK’s man-made greenhouse gas emissions.
How has this changed?
Since the industrial revolution (around AD 1750) atmospheric concentrations of a number of greenhouse gases have increased, thus increasing their greenhouse effect.
- Carbon Dioxide : Up by 30%
- Methane : Up by 150%
- Nitrous Oxide : Up by 16%
Why have these gases increased?
The changes are largely due to human activities, primarily fossil fuel use, land-use change and agriculture.
In 2005,
- 37 per cent of carbon dioxide emissions were from energy industries,
- 22 per cent from road transport,
- 18 per cent from other industries and 15 per cent from residential fossil fuel use.
Atmospheric levels in the UK have increased from a pre-industrial level of 280 parts per million (ppm) to 365 ppm (1998 figures).
What effect has this had on our global temperatures?
Over the past century global temperatures have increased on average by around 0.7 degrees centigrade. This takes us out of the range of average temperatures experienced on Earth over the last 1000 years. 1998, for example, was the hottest year in the 20th century since global records began in 1850. Studies of this trend show that it is statistically significant, cannot be explained by natural climate variation alone and is primarily caused by human activities.
What about the future?
The third working group report to the UN Intergovernmental Panel on Climate Change in April, 2014, noted that
- global emissions of greenhouse gases have risen to unprecedented levels despite a growing number of policies to reduce climate change. Emissions grew more quickly between 2000 and 2010 than in each of the three previous decades.
- without additional efforts to reduce Greenhouse Gas emissions beyond those in place today, emissions growth is expected to persist driven by growth in global population and economic activities.
- without additional mitigation, global mean surface temperature will increase in 2100 from 3.7 to 4.8°C compared to pre‐industrial levels
The report pointed, therefore, to the increasing urgency to introduce measures for both mitigation and adaptation.
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