Like our day-to-day weather, climate change is a very complex subject. The media provides us with reports about global warming but it can be difficult to form an objective opinion when other scientists put forward what look like opposing views.

What we need to understand is that these views are just other climate change scenarios and nothing is set in stone. The latest thinking is that the world is warming up, but how this will affect us in the future is difficult to qualify. All scientists agree that the world is warming- the debate is centred on how much is due to human activity.

The weather elements at a given location will vary from day to day and from year to year, but generally are expected to remain within set limits over a long time period. This is known as our climate. This natural variability ensures we have cold and warm years.

When we talk about global warming, we talk about the 'greenhouse effect'. This is actually a natural and essential feature of our atmosphere without which our planet would be uninhabitable. This process works by the principle that certain atmospheric gases, (or greenhouse gases) allow short wave radiation from the sun to pass through them unabsorbed, while at the same time absorbing some of the long wave radiation reflected back to space. The net result; more heat is received from the sun than is lost back to space, keeping the earth's surface some 30 to 35C warmer than it would otherwise be.

The problem is that man is adding to and changing the levels of the gases responsible for the greenhouse effect and is therefore enhancing this warming.

Globally 1998 was the warmest year ever recorded and eight of the ten warmest years fell in the last decade. Global ice sheets have decreased, so has global snow cover. During the earth's history there have been warmer periods, millions of years ago. However this is the most rapid rise in temperature since the end of the last ice age. So evidence is mounting that we, mankind are affecting the global climate, and the current warming has exceeded the natural fluctuations.
Carbon dioxide (CO2) is the gas most significantly enhancing the greenhouse effect. Plant respiration and decomposition of organic material release more than 10 times the CO2 than released by human activities, but these releases have generally been in balance during the centuries leading up to the industrial revolution. Since the industrial revolution amounts have increased by 30%. Other greenhouse gases include Methane, Nitrous oxide, CFC's (manmade) and Ozone. One major problem is that these gases can remain in the atmosphere for decades.

The combustion of fossil fuel (oil, natural gas and coal) by heavy industry and other human activities, such as transport and deforestation, are the primary reasons for increased emissions of these gases.

In order to try and predict possible consequences of this warming for the future, research institutes use climate modelling to simulate the climate and oceans over many decades.
So far model simulations point to global temperature rises of approximately 3 degree C in the next 100 years, which doesn't sound much. Consider however that the difference between average global temperatures now and the last ice age (not strictly correct but sounds better!) some 20,000 years ago is only around 6 to 8C.

Climate models also predict changes in rainfall and continued rise in sea level. Sea level rises will be due to thermal expansion of the ocean along with the melting glaciers and mountain snow and ice. The best estimate is 50cm by 2100, but this will vary considerably with location. Think about Bangladesh where 37% of the land lies below 3 metres and the effect of storm surges.

It's difficult to ascertain whether the world weather is becoming or will become more extreme. The scenario of more storms, hurricanes, tornadoes etc is far from proven, although indications from the Hadley Centre are for a greater frequency of deep Atlantic depressions.The consequences of these changes are far reaching.

Consider for example that floods and droughts are likely to increase in number and severity. Diseases, such as malaria, spread by mosquitoes depend on local climate, especially temperature. Different flora and fauna flourish under various climate regimes, but cannot respond quickly to change. Nature reserves, often established to protect particular species may no longer be located within a climate hospitable to that species, making them prone to disease and pests.Humans are more adaptable to different climates, but heat and water stress are likely to become more of a problem.

Uncertainties in future predictions arise due to imperfect estimates of future emissions of greenhouse gases and sulphur, which in turn depend on population growth, energy demand, economic factors.

What can we do to slow down this warming? By sharing technologies, experience and resources we can hopefully lower the greenhouse gas emissions and reduce the threat of global climate change. Choose clean energy options where available, such as wind, solar and wave power, these do not emit greenhouse gases and are renewable. Individually, we can recycle material, insulate our homes, take public transport and think about energy efficiency in the home.

The effects of global warming and a changing climate will not be felt equally across our planet. Poorer nations are generally more vulnerable to the consequences.

We are confident that putting more carbon dioxide into the atmosphere will lead to a continued warming of the earth's surface. However there will be consequential changes in the climate system which will either magnify or reduce the rate of warming.

Our incomplete understanding of this feedback leads to substantial uncertainty in the predictions.So what has been written here is more an indication of what change can be expected as opposed to a firm forecast. A balance is needed between the needs of the living and our obligations to future generations.

source: bbc.co.uk By Helen Willetts