The retreat of the Arctic ice is clearly visible in this composite, comparing 2007 levels (top) to 2005 (bottom)

The leaking of emails and other documents from the Climate Research Unit (CRU) at the University of East Anglia, UK, has led to a media and political storm. The affair is being portrayed as a scandal that undermines the science behind climate change. It is no such thing, and here’s why.

We can be 100 per cent sure the world is getting warmer

Forget about the temperature records compiled by researchers such as those whose emails were hacked. Next spring, go out into your garden or the nearby countryside and note when the leaves unfold, when flowers bloom, when migrating birds arrive and so on. Compare your findings with historical records, where available, and you’ll probably find spring is coming days, even weeks earlier than a few decades ago.


You can’t fake spring coming earlier, or trees growing higher up on mountains, or glaciers retreating for kilometres up valleys, or shrinking ice cover in the Arctic, or birds changing their migration times, or permafrost melting in Alaska, or the tropics expanding, or ice shelves on the Antarctic peninsula breaking up, or peak river flow occurring earlier in summer because of earlier snowmelt, or sea level rising faster and faster, or any of the thousands of similar examples.

None of these observations by themselves prove the world is warming; they could simply be regional effects, for instance. But put all the data from around the world together, and you have overwhelming evidence of a long-term warming trend.

We know greenhouse gases are the main cause of warming

There are many ways, theoretically, to warm a planet. Orbital changes might bring it closer to its star. The star itself might brighten. The planet’s reflectivity – albedo – can change if white ice is replaced by darker vegetation or water. Changes in composition of the atmosphere can trap more heat, and so on.

It could even be that Earth isn’t really warming overall, just that there has been a transfer of heat from the oceans to the atmosphere.

Researchers have to look at all of these factors. And they have. Direct measurements since the 1970s make it certain, for instance, that neither the sun’s fluctuating brightness nor changes in the number of cosmic rays hitting Earth are responsible for the recent warming. Similarly, direct measurements over the past century show that the oceans have warmed dramatically. The planet as a whole is getting warmer.

That leaves the rising levels of greenhouse gases in Earth’s atmosphere – which have been directly measured – as the main suspects. Working out how these changes should affect the planet’s temperature in theory is extremely complicated. The only way to do it is to plug all the detailed physics into computers – create computer models, in other words. The results show that the only factor that produces anything like the temperature rise seen is the observed increase in greenhouse gases.

How do we know the models aren’t wrong? From studies of past climate. To take one example, ice cores drilled from the Antarctic ice-sheet show a surprisingly close correlation between greenhouse gas levels and temperature over the past 800,000 years.

During this time, greenhouse gases have never risen as high or as fast as they are now. That means there is still a lot of uncertainty about the extent of future warming – estimates of the effect of doubling CO 2 , including all feedback processes, range from 2°C to 6°C. But the big picture is clear.

Is it possible that tens of thousands of scientists have got it wrong? It is incredibly unlikely. The evidence that CO 2 levels are rising is irrefutable, and the idea that rising levels lead to warming has withstood more than a century of genuine scientific scepticism.

So why are scientists “fixing” the temperature data?

Some of the contents of the hacked material, such as the “Harry_read_me.txt” file, might appear shocking, with its talk of manipulation and “tricks”. But raw data almost always has to be “fixed”.

For example, suppose you and your neighbour keep a record of the temperature where you live, and decide to combine your records to create an “official” record for your locality. When you compare records, however, you’re surprised to find they are very different.

There are many reasons why this might be so. One or other thermometer might be faulty. Perhaps you placed your thermometer in an inherently warmer place, or where it was sometimes in direct sunshine, or took measurements at a different time of day, and so on. To combine the two records in any meaningful way, you’ll need to adjust the raw data to account for any such factors.

Not doing so would be pretty dumb. Where possible, scientists should always look at their data in the context of other, comparable data. Such scrutiny can often reveal problems in the way one or other set of data was acquired, meaning it needs adjusting or discarding. Some apparent problems with the predictions of climate models, for example, have actually turned out to be due to problems with real-world data caused by the failure to correct for factors such as the gradual changes in orbits of satellites.

The tricky question is where to draw the line. There is a continuum from corrections based on known problems (essential), to adjustments based on probable errors in the data (good practice as long as all assumptions are made clear), to adjustments done solely to make the data fit a hypothesis (distinctly dodgy).

It remains to be seen if any of the adjustments described in the hacked material fall into this last category. But the mere fact that the leaked material reveals climate researchers “fixing” data is not proof of fraud. Manipulating data is what scientists do.

But what about that “trick” to “hide the decline”?

One of the leaked emails refers the “trick” of adding the real temperatures, as recorded by thermometers, to reconstructions of past temperatures based on looking at things such as growth rings in trees.

The problem is that some sets of tree-ring data suggest temperatures start falling towards the end of the 20th century, which direct temperature measurements show was not the case. So the researchers instead replaced the reconstructed temperature data for this period with the directly measured temperature data.

Is this an unjustified “fix”? No, because some sets of tree-ring data can be compared with the direct records of local temperature for the past century. Up until the 1960s, there is a very close correlation between the density of growth rings in trees in northern latitudes and summer temperatures, but after this it starts to break down.

We don’t know why. It might be that the correlation breaks down whenever it gets too hot, in which case reconstructions of past temperature that rely heavily on tree-ring data will give a misleading picture. Or it might be due to some factor unique to the 20th century, such as changes in the timing of the snow melt, in which case it will not affect reconstructions.

The issue has not yet been resolved but there has been no attempt to conceal this or any of the many other problems with temperature reconstructions. On the contrary, the head of the Climate Research Unit at East Anglia, Phil Jones, and others have published papers discussing it in prominent journals such as Nature.

What really matters is not how hot it is now or how hot it was a few hundred years ago, but how hot it is going to get. Campaigners have highlighted temperature reconstructions like the “hockey stick” graph because they are easy for people to understand, but in scientific terms they are not of great significance. We know the world is warming and we know that the main cause is rising CO 2 levels. So with CO 2 levels rising ever faster, we can be sure things are going to get a lot hotter.

But surely any attempt to block publication of sceptical scientific papers is indefensible?

Some of the leaked emails reveal the climate researchers’ unhappiness with the publication of certain scientific papers questioning the global warming consensus, and discuss removing journal editors they perceived as being sympathetic to global warming sceptics.

This sounds horrifying to some non-scientists. But many are confusing two very different things: attempting to block publication in certain scientific journals and the suppression of information.

Scientific journals are only supposed to publish papers that meet certain scientific standards. Researchers work for years on papers and then submit them to the top journals in their field. The editors select the ones they think are most important or noteworthy, and send them to a handful of reviewers – scientists working in the same areas. Each reviewer sends back a report suggesting acceptance, rejection or revisions, and the editor decides whether to publish based on these reports. Most papers sent to leading journals get rejected.

This system of “peer review” has its critics, but is generally regarded as the least-worst system to ensure the quality of published scientific research. Researchers whose work is rejected can resubmit their papers to other, less high-profile journals. Failing that, anyone is free to publish their views on global warming online, or in books and newspapers if they can.

Many leading scientists think that the papers mentioned in the emails had serious scientific flaws and possibly should not have been accepted by the journals in question. If this were the case, it would raise questions about the role of the editors at those journals. It is hardly outrageous behaviour to call for the replacement of people who are, in your personal view, not doing their jobs properly.

What about apparent attempts to avoid freedom of information requests?

In some emails, Jones – who has stepped down pending a review of what went on – discusses ways not to fulfil requests made under the UK’s freedom of information laws. In one, he calls on other researchers to delete certain emails. While on the face of it this does not look good, whether any researchers broke any laws or breached any university guidelines remains to be determined.

In other cases, however, it is clear that researchers could not comply with freedom of information requests because they did not have the right to release all the data in question. There is also no doubt that climate change deniers have been using freedom of information requests to harass researchers and waste their time, with the CRU receiving more than 50 such requests in one week alone this year.

What’s more, individual researchers have little to gain from giving away data and software they have spent years working on. Scientific careers depend on how many papers you publish. If you keep data to yourself, no one else can publish papers based on it before you do.

This does not mean researchers should be allowed to hold onto their data. It is undoubtedly in the public interest for there to be full disclosure of the measurements upon which climate scientists are basing their conclusions. In fact, much of it is already freely available. But the pressures climate researchers are under does help to explain why many are so reluctant to make all data public.

Clearly, the leaked emails have caused disquiet in some quarters. There’s no doubt there are concerns about the content of some of the emails – even when you know the way science really works – as laid out above. The Intergovernmental Panel on Climate Change and the University of East Anglia are now holding investigations to determine if anything unethical did go on. But nothing in them justifies claims of a massive conspiracy, or undermines the certainty about climate change and its causes.