What is Climate Change? Print Digg Digg Facebook Facebook Twitter

Climate change is the result of greenhouse gases (GHGs), principally carbon dioxide, building up in our atmosphere and helping to trap heat.  According to the vast majority of the world's scientists this has caused the climate to change globally.

Over the past two decades, the evidence that GHG is continuing to build-up as a result of human activities has become conclusive i.e. these changes have come about as a combined effect of increases in emissions, such as fossil fuel burning, and decrease in carbon sinks, such as reduced forest cover.


The Intergovernmental Panel on Climate Change (IPCC) is the leading international scientific body for the assessment of climate change. Thousands of scientists from all over the world contribute to the work of the IPCC on a voluntary basis.  

The Working Group Summary was published in February 2007 and assesses the current scientific knowledge of the natural and human drivers of climate change, observed changes in climate, the ability of science to attribute changes to different causes, and projections for future climate change.

The report was produced by 620 authors and editors from 40 countries, and reviewed by more than 620 experts and 113 governments.

The Report states:


"Warming of the climate system is unequivocal."

  • "Most of the observed increase in global average temperatures since the mid-20th century is very likely  i.e. over 90% likely, due to the observed increase in anthropogenic greenhouse gas concentrations."


Changes in the atmosphere

Carbon dioxide, methane, and nitrous oxide are all long-lived greenhouse gases.

  • Carbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values.
  • The amount of carbon dioxide in the atmosphere in 2005 (379 ppm) exceeds by far the natural range of the last 650,000 years (180 to 300 ppm).
  • The amount of methane in the atmosphere in 2005 (1774 ppb) exceeds by far the natural range of the last 650,000 years (320 to 790 ppb).
  • The primary source of the increase in carbon dioxide is fossil fuel use, but land-use changes also make a contribution.
  • The primary source of the increase in methane is very likely to be a combination of human agricultural activities and fossil fuel use. How much each contributes is not well determined.
  • Nitrous oxide concentrations have risen from a pre-industrial value of 270 ppb to a 2005 value of 319 ppb. More than a third of this rise is due to human activity, primarily agriculture.


Warming of the planet

  • Cold days, cold nights, and frost events have become less frequent. Hot days, hot nights, and heat waves have become more frequent. Additionally:
  • Eleven of the twelve years in the period (1995–2006) rank among the top 12 warmest years in the instrumental record (since 1850, towards the end of the Little Ice Age).
  • Warming in the last 100 years has caused about a 0.74 °C increase in global average temperature. This is up from the 0.6 °C increase in the 100 years prior to the Third Assessment Report.
  • Observations since 1961 show that the ocean has been absorbing more than 80% of the heat added to the climate system, and that ocean temperatures have increased to depths of at least 3000 m (9800 ft).
  • Average Arctic temperatures increased at almost twice the global average rate in the past 100 years.
  • Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1300 years (including both the Medieval Warm Period and the Little Ice Age).


Source http://en.wikipedia.org/wiki/IPCC_Fourth_Assessment_Report#Observations




The Science of Climate Change

This document aims to summarise and clarify the current understanding of the science of climate change. You can download here






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