Climate change explained

The great US state of Utah has passed a Bill declaring that climate science is "questionable," that the world is not warming and which demands that all efforts to reduce greenhouse gas emissions be halted until such time as they can be satisfied that all this talk of climate change isn't just hogwash.

During the debate it was declared there was a vast conspiracy aimed "to destroy the American way of life and control world population through forced sterilisation and abortion." Who'd have thought a ban on solar panels could prevent abortions? You learn something every day.

With the rise in the misnamed "climate sceptic" movement perhaps now is a good time to take a look at why scientists think that climate change is a clear and present danger. This is not a scientific paper, so I'll try to avoid using jargon like "southern oscillation index" - except for just then, obviously.

The first question to ask is - "is the world getting warmer?"

There has been consistent monitoring from more than 15,000 fixed stations dotted around the world for some time now.

We have reliable records of directly measured global temperatures going back to 1850, although climate monitoring in some form has been going on since 1697.

There are also a number of ways in which we can estimate global temperatures going back thousands upon thousands of years using tree rings, corals and ice cores, which all show that we are in a distinct period of global warming. But let's confine ourselves to this most recent monitoring.

While there can be disagreement and debate over modelling, the significance of certain results and other areas of the science, there is no significant dispute over this data.

And the data is very clear, despite the fact that there is always variation from year to year, the trend of these directly measured temperatures is that the world is getting hotter.

The temperature over this period has changed by 0.8?C, which sounds relatively small although this conceals within it some extremes and significantly shifting of weather patterns.

When you think about the fact that the last ice age saw a temperature difference of 5?C and that meant large parts of Europe were under a thick layer of ice, it's clear that these small differences can make a large impact.

It's also worth drawing out the fact that over this 150-year period, the 10 hottest years were 2008, 2007, 2006, 2005, 2004, 2003, 2002, 2001, 1998 and 1997. You may detect a pattern there.

The next question to ask is - "what effect is this change having?"

There are a number of dire predictions about what may happen over the next 200 years, but let's leave those aside for the moment and look at some of things that are happening now.

For example, those living in Greenland are watching as their glaciers are receding at a rapid pace, something that has visibly increased since the year 2000.

When you are watching the ice recede before your eyes you don't really need numbers to back up the evidence.

I don't live in Greenland, but suspect that having less ice around might not lead to a drastic cut in their quality of life.

However, the same cannot be said of parts of Africa which are visibly drying and the impact of climate change on the great lakes are threatening the crops and livelihoods of large numbers of very poor people.

Many weather events are directly influenced by the temperature of the oceans. The increasing ferocity of hurricanes across the Americas, coupled with historic levels of La Nina and El Nino in south America have seen tens of thousands displaced and significant loss of life over the last 10 years.

Then we look at the direct impact in Australia which is facing water shortages and forest fires in a way it has never experienced before.

Then there is the flooding in Bangladesh that is directly related to rising sea levels, caused by the melting ice at the poles.

All of these new phenomena, and the hundreds I have no space to list, are observable with the naked eye and directly linked by what we know about temperatures across the globe.

So the final question to ask is - "why is the world getting warmer?"

Some people are saying that these changes may well be natural, but is this credible?

There certainly have been naturally occurring changes in our climate. The difficulty for the sceptics on this one is that the natural causes that effected the climate were scientifically observable.

For example, previous warm periods were caused by, well, increased levels of greenhouse gases.

Currently it is the way we run our economy that is the prime contributor of these gases.

Why do scientists think it might be gases? The greenhouse effect is a well established phenomenon and one without which the world would be uninhabitably cold.

Essentially the atmosphere acts like a blanket, trapping the sun's heat. This is a good thing.

Greenhouse gases, carbon dioxide being the one most often referred to, thicken that blanket and when events like volcanic eruptions or the industrial revolution occur, the amount of greenhouse gases in our atmosphere increase, like extra layers of blanket, inevitably making the world warmer.

However, the climate is complex and even though the world is warmer overall, the effects are felt in different ways in different places.

For example, many people think that there may come a point when the warm water ocean current known as the Gulf Stream may change course and Britain will actually become much colder and wetter as a result even while Australia becomes drier and hotter. What a shame we couldn't swap effects.

Some greenhouse gases are man-made, some are naturally occurring and others have been trapped by nature and are gradually beginning to release into the atmosphere due to warming temperatures, speeding up the effect.

This mainly involves ice and ocean sinks where the oceans or ice have trapped naturally occurring carbon over thousands of years but begin to release this carbon back into the atmosphere as the temperatures warm.

So as the blanket thickens it creates a process where even more blankets get thrown on top of us. If you have need of a good cry you can go and read documents like Defra's Adapting To Climate Change, which is the scientific equivalent of Private Fraser's "we're all doomed."

Alternatively, you could join the movement to take some of the blankets off again and next week I'll be taking a look at how exactly we might be able to do that.