What do we mean by climate and climate change?

Climate is the average of weather over time and across large regions, even the entire planet. The global climate has always varied for many reasons, such as interactions between components in the climate system oceans, atmosphere, ice sheets, etc. A climatic phenomenon where the surface temperature of the eastern Pacific Ocean warms affecting the weather worldwide is an example of this. Climate change, on the other hand, occurs because the amount of energy in the entire climate system is changed which affects each and every component in the system. Changes in the Earth’s orbit, the energy received from the Sun and the amount of greenhouse gases in the atmosphere can all cause climate change.

How can humans cause climate change?

Human activities such as burning fossil fuels increase the amount of CO2 and other greenhouse gases in the atmosphere, enhancing the natural greenhouse effect. Increasing CO2 causes the planet to heat up. Ice cores show the concentration of CO2 in the atmosphere has increased by at least 40% in the last 200 years since the Industrial Revolution. The last time CO2 increased this much was over a 6,000 year period as the Earth came out of an ice age, and the average surface temperature rose by 5C. Burning fossil fuels and changes in land use, such as deforestation, have altered how much sunlight is reflected back into space called the albedo. Small particles like smoke and dust in the atmosphere can reflect sunlight and affect clouds. The impact this has on the climate is only beginning to become clear, and is expected to feature prominently in the IPCC’s 5th Assessment Report in 2014.

What effects will human activity have on the climate?

It will get warmer, but the exact climatic effects of the recent dramatic increase in CO2 are not certain. So far we have seen an increase of 0.8C in the average surface temperature of the Earth since 1900, with melting in the Polar Regions and more frequent extreme weather. Simple calculations and our most complex models all agree: if we double CO2 we will see an average warming of between 2 and 4.5C. In context, 4.5C is the difference between today and the deepest ice-age. Models of the climate system make varying predictions of future temperatures and other effects of climate change because of two major factors:

  • Climate sensitivity.

Once the climate begins to change, the effects of that change can lead to further changes. This makes exact effects hard to predict. So if we double CO2, we cannot know exactly what the average increase in temperature will be.

  • Future emissions.

We don’t know how successful we will be in reducing greenhouse gas emissions.

Why does climate change matter?

Small changes in average temperature can translate to big changes across the planet, leading to rising sea levels, more extreme weather and some areas becoming much harder to live in. Plants, animals, humans and societies have developed in a climate that has varied only a little, except over extremely long timescales: we are not adapted to cope with rapid climate change. See overleaf for common misconceptions about climate change

Common misconceptions about climate change

  1. Not all scientists think man-made climate change is real.

The vast majority of climate scientists agree on the fundamentals of human-induced climate change, though  there is healthy debate about the extent of change and what to do about it. Just as with smoking and lung cancer, the weight of evidence strongly suggests that human factors have caused and will cause climate change. All national academies of science agree on the existence of man-made climate change, while most scientists who disagree work outside climate science.

2.Climategate and scientific misconduct

Three independent inquiries into the release of hacked emails from the University of East Anglia, which were used to suggest global warming was a scientific conspiracy, recommended greater transparency by UEA but found nothing wrong with the science.

3.The UK has had cold winters and poor summers

Weather is not climate and we must look at averages. It is risky to jump to conclusions about climate change by looking at small areas like the UK. At the global level, local variations average out and it is easier to make clear statements. Nonetheless, 7 of the 10 warmest years in the UK since 1910 have occurred between 2001 & 2012.

  • Extreme weather:

Climate change also raises the likelihood of extreme weather events. For instance, floods which we have come to expect once in 100 years are now likely to be seen once in 10 years and severe thunder storms are 20% more likely than 20 years ago. This is supported by observations.

  • There has been no global warming since 1998’

1998 was a particularly warm year so is an unfair place to start measuring recent trends. But every decade since the 1950s has seen warming and 2000-2009 was around 0.15C warmer than 1990-1999. Temperature fluctuates naturally, but the general trend is upwards and it moves in a series of jumps. However, the rate of rise does appear to have slowed in the last decade and we don’t yet know exactly why.

  • Climate change has happened before

Variations in the climate have occurred, such as the Medieval Warm Period and Little Ice-Age. There could be various causes, e.g. solar activity. But that does not change the fact that more CO2 will cause warming.

  • Warming is causing more CO2, not the other way round

Ice-core records do indeed show that CO2 levels rise when the Earth comes out of an ice-age. However, warming and CO2 levels cause each other, so if either happens the other will follow. We’re doomed, and there’s nothing we can do about it. Some claims about the severity of climate change have gone beyond hard evidence. For instance, climate change has been speculatively linked to high numbers of deaths, and it has been claimed we are close to catastrophic ‘tipping points’. While tipping points are genuine scientific possibilities they are hard to predict with any certainty. Meanwhile, there is much we can do to prepare for and to slow climate change.

  • Climate change will have some good effects

Small increases in CO2 may increase crop yields but larger increases will affect which crops can grow. Some colder areas will become more pleasant, but such benefits will be outweighed by rising seas, heat and drought.

What does the future hold?

How the climate changes in the future will go beyond what we have already seen and the largest effects will be in temperature-sensitive regions like the poles. Long timespans are needed to let the planet adjust. For instance, if the Greenland ice-sheet completely melts, sea levels will rise by many metres over an unknown length of time. As CO2 levels increase, the risks associated with climate change become more serious.

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