The Earth's atmosphere is made up of a blanket of gases, which trap enough heat to sustain life. However, by burning fossil fuels and cutting down forests humans pump billions of tonnes of carbon dioxide (CO2) into the atmosphere. We also add other gases to the atmosphere in smaller quantities.
These emissions increase the 'greenhouse effect', adding to the natural
canopy of gases in the atmosphere and causing more heat to become
trapped. As a result, the global temperature is increasing,
throwing the world's climate out of balance.
The extra carbon
dioxide gas we are adding to the atmosphere is mostly from burning
large amounts of fossil fuels for energy production and
transport.
Changes in land use and deforestation also
release more carbon dioxide into the environment. Trees, for example,
are natural 'carbon sinks' - they absorb carbon dioxide - and when they
are destroyed, carbon dioxide is released into the atmosphere.
What's changed?
While
many greenhouse gases occur naturally, the rate humans are adding them
to the atmosphere is far from natural. It is estimated that
concentrations of carbon dioxide are now more than one third higher
than before the industrial revolution, when the large scale burning of
fossil fuels and modern industry and agricultural practices began,
adding to the atmospheric levels of naturally occurring gases such as
carbon dioxide, methane and nitrous oxide. Humans are also creating
new, very potent greenhouse gases such as hydrofluorocarbons (HFCs)
from industrial activities.
Even if all greenhouse gas
emissions were stopped today, the effects from past activities will
persist for many centuries, due to the long life of greenhouse gases in
the atmosphere and the long time required for transfer of heat from the
atmosphere to the deep oceans.
What this means is that
every day the amount of warming gasses in the atmosphere increases with
inevitable consequences - making it harder and harder for us to reign
in climate change. For now, though, we still can largely choose
our climate future.