In their rush to appear “greener than thou” this week, each of the main parties has made valuable contributions to the debate over climate change, and some fairly ridiculous ones too.

David Miliband, the Environment Secretary, rightly pointed out that domestic energy use accounts for five times the carbon emissions of aviation, and is thus a bigger priority. The Government, though, was crass to accuse the Conservatives of seeking to “criminalise” flying with new taxes.

Both opposition parties are justified in pressing the Government for more ambitious targets than the 60 per cent emissions cut set for 2050. Binding annual reductions, however, may not be the best way to achieve this: as ministers said, a cold winter could make this disastrous for consumers.

But for all the point-scoring that surrounded yesterday’s draft Bill, a more promising theme has shone through. More striking than the crude caricature has been the extent to which all the parties are now agreed on the need for a more robust legislative approach to global warming.

The argument is no longer about the rationale for cutting greenhouse gas output, but about how this should be achieved. It is now recognised that the details are where votes are to be won.

In this, politics has caught up with science, albeit a decade or so late. For notwithstanding the enduring objections of a small band of scientific sceptics, such as those who contributed to the Channel 4 programme The Great Global Warming Swindle, the evidence that the world is getting hotter and that humans are responsible has become overwhelming.

As in politics, there is still room for debate over the intricacies of what is happening and what should be done about it, but the wider issue is largely settled.

The consensus that human-induced global warming is more than a hypothesis is built chiefly on the work of the Inter-governmental Panel on Climate Change. Its most recent report, published last month, included contributions from more than 2,500 scientists, and concluded with 90 per cent certainty that human activities are responsible for rising world temperatures. A further increase of between 1.1C and 6.4C (11.5F) is predicted for the end of the century.

As the critics say, the sheer number of eminent scientists who have signed up to such a view does not automatically make it right. It is possible, if improbable, that so many clever men and women could be wrong.

What this ignores, however, is the greatest strength of the panels’ report: its multidiscipli-nary approach. The most compelling reason for believing global warming to be a genuine problem is that the theory is consistent with evidence emerging from a multitude of different fields. Everyone knows about the atmospheric temperatures, but that is only one part of a much bigger story.

Ice cores from Antarctica show that temperatures have fluctuated with carbon dioxide levels for 750,000 years. Ocean temperatures show warming signatures that are inexplicable without anthropogenic greenhouse forcing. Animal distribution and behaviour is changing in line with the theory. The same signals can be seen in atmospheric physics, botany, meteorology, geography, ecology and many other scientific disciplines. Thousands of scientists may be mistaken — but across so many diverse fields?

Against this pretty consistent picture, the sceptics have mustered only isolated strands of contradictory evidence. For the most part, these have turned out to be artefacts of badly handled data, but such revelations have prompted no more than a change of tune.

For years, sceptics pointed to discrepancies between temperatures in different parts of the atmosphere. When these were conclusively resolved, the line became that the world might be warming, but humans aren’t responsible. Maybe the culprit is sunspots, not CO2. Now the theory du jour, to which Channel 4 gave pride of place, is cosmic rays, though meteorologists vigorously dispute the effect on cloud cover that these are claimed to have. Gavin Schmidt, of Nasa, has decribed the idea as “by far the most blatant extrapolation beyond reasonableness that we have seen”.

There is an analogy worth making here, with another branch of science that causes unwarranted controversy, if to a lesser extent in Europe than in the US. The fact of evolution is also based on evidence not from one discipline, but from 20 or more. If the principle is wrong, then so are most of the fields of zoology, botany, palaeontology, genetics, molecular biology, geology, anthropology and medicine — to name but a few through which it traces a common thread.

The deniers of global warming and evolution are right that science is not always best decided by a consensus of individuals. The consensus that matters is one of data from many sources — but that stands powerfully against them too. So, now, do Britain’s mainstream politicians. It is great to see them squabbling over what the science means for policy, and not hiding behind a critical fringe to sit on their hands.

The targets

-Legally binding five-year carbon dioxide emission targets

-First three targets to be set by December 31, 2008; first target period to cover 2008-12

-Statutory 2020 target of 26-32 per cent emissions reduction Statutory 2050 target of 60 per cent emissions cut

-Aviation and shipping excluded

-Committee on climate change to be appointed. Ministers must take its advice into account

-Powers granted to ministers to introduce secondary legislation as required to meet targets

-Annual reporting to Parliament

-Maximum of 50 per cent of carbon credits can be purchased from abroad

The reaction

With climate change we can’t just close our eyes and cross our fingers
David Miliband

In the end the real prize is not just to get the Europeans in but the Americans, the Chinese and the Indians too
Tony Blair

Their insistence on mediocre and dangerous targets means all their efforts don’t go far enough
Sian Berry, Green Party

The announcement goes nowhere near far enough
Miles Seaman, Institution of Chemical Engineers

The draft is a good start but needs to acknowledge the 2C global warming danger threshold
Ashok Sinha, director, Stop Climate Chaos

A disproportionate burden falls on business
Miles Templeman, director-general, Institute of Directors

Businesses accept the part they must play
David Frost, British Chambers of Commerce

The technology exists to clean up emissions
Professor Peter Styring, University of Sheffield

Transport is the most challenging sector, in which carbon emissions continue to grow
Sue Ion, vice-president, Royal Academy of Engineering

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