The Greenhouse Effect

The Greenhouse Effect

First identified almost 200 years ago, it describes the ability of some gasses to reabsorb thermal radiation reflected from the surface of the earth. Without greenhouse gasses this energy would be reflected back into space and we would be in big trouble. The earth's average temperature would be about -18^oC, more than 30 degrees below the current average surface temperature of 14-15^oC and it would mean the planet would be a lifeless ball of ice.

The four major gasses involved are:

• water vapour 
• carbon dioxide
• methane
• ozone

 Apart from water vapour, these gasses are present in tiny quantities.

For example, historically, concentrations of carbon dioxide have been between180 and 220 parts per million (ppm) for millions of years. Today, levels are around 390ppm - and over half the rise has happened in the last 50 years. CO² concentration is rising by about 17 ppm each decade - concentrations will have doubled by 2030 and that will cause a 3^oC rise in global mean temperature.

Although the overall changes in recorded temperature are relatively small, geological evidence suggests that the window for a tenable climate is also surprisingly small. To put a three degree rise in perspective - the difference in global temperatures between periods of glacial and interglacial eras is reckoned at no more than 5^oC.

Global warming

Refers to the rises in global temperatures observed since the mid 20th century. There is a strong scientific consensus that these rises are man-made (anthropogenic), caused by rising concentrations of greenhouse gasses such as carbon dioxide and methane. Global warming is a cause of climate change - it does not mean the weather will be warmer! It would be more accurate to say it causes “more weather” - because really, global warming means there's more energy in the system that drives the world's weather.

At the moment we could be facing between 2 and 3^oC of warming. It doesn't sound like much, but the amount of extra energy it takes to force that rise over something as big as an entire planet is vast. It's this increase in available energy that drives climate change.

How Global Warming Changes the climate

To get an idea of how it works. imagine the world's climatic influences; great oceanic currents, jet streams, etc, are like a giant engine that powers weather systems around the planet. Incoming solar energy can be treated as fuel and the greenhouse gasses as a carburettor. More greenhouse gas in the system is akin to pressing harder on the accelerator of the car - making it "go faster" and as a result, less stable and more prone to a crash.

Weather systems are complex and it is difficult to predict exactly how they will be affected but one of the most probable effects of global warming will be to intensify the weather we experience at the moment. That could well mean more rain, bigger storms, hotter, longer, droughts and colder more intense winters. More and more of these severe weather events are happening. It's almost impossible to say the droughts that badly affected last years grain harvests around the world or the disastrous floods across Asia and Australia are directly due to climate change - but they are exactly the kind of results climatologists have predicted.

A NASA animation of global temperature changes over the last 100 years showing warming over the last 2 decades

Should we worry?

Concerns about global warming don't stop with changes to the weather. Warming has been greater in polar regions and the melt rate of the ice cap has accelerated far more quickly than predicted. Melting ice caps will certainly cause sea level rises and recent studies suggest this is happening far more quickly than expected. Beyond these highly predicable effects, there is a whole tranche of other possible problems that start to read like the background to a dystopian Sci Fi novel.

No one fully understands how the world's climate systems work, but it is believed that the great oceanic currents, responsible for moving vast quantities of energy around the globe, are driven by icy cold salt water descending deep into the ocean and flowing south. If the density of this cold water is reduced by fresh melt water from the ice cap diluting its salt content, it could “switch off” the gulf stream, triggering a new ice age in Northern Europe.

Another great unknown in the global warming equation are the effects rising temperatures will have on oceanic and biological “carbon fixing” (locking carbon dioxide into biomass and in solution in the world's oceans). Warming in the far north could start to thaw tundra permafrost which would release methane – a far more potent greenhouse gas than CO². The sea's capacity to absorb CO² will be affected both by rising acidity caused by CO² in solution and increasing water temperatures (Henry's Law - the ability of water to hold gas in solution is directly proportional to temperature and pressure). At present it is believed that about a third of anthropogenic greenhouse gas emissions are absorbed by the sea. Quite apart from concerns about reducing to capacity of the worlds oceans to act as a carbon sink, the rising acidity levels are already having an effect on marine ecosystems.

Ignorance is bliss (if you are making billions from oil)

Ignoring global warming is like playing Russian Roulette with our children's future. We don't know exactly which chamber is loaded but one day, unless we move towards low carbon technology very quickly, the gun will fire. The scientific case for global warming and its connection to human behaviour is almost overwhelming but there is still great public and political scepticism, especially in the USA where “climate change denial” is being encouraged by a campaign, “funded by petro-chemical, auto, steel and utilities” (Newsweek, August 2007). Last year's well publicised “scandal” alleging the climate researchers at the climate unit of Norfolk's UEA were falsifying results (now completely disproved) was just a part of the “paralysing fog of doubt around climate change”. This campaign resembles the efforts of the tobacco industry to cast doubt on the value of scientific evidence about the dangers of smoking by well targeted lobbying, media campaigns and emotional appeals to public scepticism. The carbon literate need to understand the politics surrounding climate change as well as the science. A world that moves towards low carbon technology is a world that will be far less profitable for the interest groups who are funding the denial campaign