27/09/2013 12:26 BST | Updated 27/11/2013 05:12 GMT

David Cameron Is Failing to Show the Leadership Britain Needs to Tackle Climate Change at Home and Abroad

The report by the UN Intergovernmental Panel on Climate Change (IPCC) is a stark reminder of the scale of the challenge we face to preserve our planet for future generations.

The findings by the world's leading climate experts make for sobering reading. By the end of this century sea levels are expected to rise up to 82cm and temperatures could increase by as much as 4.8ºC.

The world cannot emit more than a total 880 gigatonnes of carbon if we want to avoid dangerous levels of climate change beyond 2ºC. Roughly 530 gigatonnes had already been emitted by 2011.

With this in mind, there are three lessons we need to draw from if we want to move forward: that the science is now beyond dispute, but we are losing ground in our efforts to tackle climate change at home and the UK desperately needs to redouble our efforts abroad.

The first lesson is the most basic but the most important: we must respect what the experts have to say. The IPCC's report marks a strengthening of the scientific consensus that climate change is happening and that humankind is responsible.

The scale of the evidence base supporting this consensus is overwhelming. The IPCC's research was authored by 800 experts, drawing on 9,200 scientific studies, including 54,000 comments from 1,000 experts from 55 countries.

Their last report six years ago said this is 90% certain. They have now upgraded that confidence to 95%. Considering that scientists will always make small allowances when making future forecasts, this is as close to a guarantee as it gets.

Of course science is always evolving and everyone is entitled to their own view. But people whose views defy reason and academic evidence are not entitled to vandalise our public response to climate change. Climate science should be left to scientists.

What do I mean by that? A few weeks ago I took part in one of the most surreal and depressing debates I have ever participated in during my time in Parliament.

It was called by the Conservative MP David Davies. He and his Tory backbench colleagues spent 90 minutes questioning whether the earth was warming at all, despite 12 of the last 15 years being the warmest ever on record. At one point we even had to discuss whether the Met Office was somehow involved in a global conspiracy to defraud the public about climate change.

The truth is that Tory sceptics have been emboldened by a disturbing change in tone from their frontbench since David Cameron entered Downing Street. He is simply failing to show the leadership we need to tackle climate change, both at home and abroad.

The administration he promised would be the "greenest government ever" now boasts an Environment Secretary who doesn't believe in climate change, an Energy Minister who has described climate change as a matter of "theology" and a Chancellor peddling a perverse false choice that we cannot combat global warming without "putting our country out of business."

This isn't just a matter of rhetoric. Think back to the last time the IPCC reported and compare the policy landscape we had then to the one we have now.

In 2007, the Stern Review - commissioned by the Labour Government - had warned just the year before of the devastating threat global warming poses to our economy. The landmark Climate Change Act, the world's first legally binding climate change target, was less than a year away from being enacted.

Fast forward to 2013 and the IPCC's fifth assessment report arrives with Britain's carbon emissions rising rather than falling. Our carbon emissions jumped by 3.9% last year - more than any other country in the EU.

Even more worryingly, the Government has failed to set a target a clean up our power system by 2030 at the same time as the independent Committee on Climate Change has warned that the UK is currently not on track to meet our carbon reduction targets.

On the world stage, the clock is ticking down until the crucial Paris climate conference in 2015. But while leaders like Barack Obama and Francois Hollande are seizing the moment, our Prime Minister is strangely silent.

David Cameron went all the way to the Arctic in 2006 to stress his personal commitment to the environment. But when given the opportunity to host a summit of world leaders at the G8 earlier this year, he chose to not include climate change on the formal agenda.

When I pressed him about this in Parliament, he retorted that he didn't see the point of having "a long conversation about climate change."

But that's the point. Climate change demands answers from us to questions that are not easy. The discussions we need to have are complex. That's why we can't afford to delay.

Britain needs to redouble our efforts at home and strain every sinew in the coming months to help secure a new global and legally-binding climate change treaty. The consequences if we don't have now been made clear for all to see.

The scientists have reached an agreement. Governments and policymakers must show they can do the same and take action now.