Early one June morning this year, along with 19 fellow activists I jumped off a Greenpeace inflatable and climbed up the vertical wall of the leg of a giant oil rig, the Leiv Eiriksson, which was drilling nearly 200km off the coast of Greenland in the freezing waters of the Davis Strait.

What, you might ask, would compel a group of relatively sensible people do such a thing?

The simple answer is this. The Leiv Eriksson is perhaps the most controversial oil rig anywhere on the planet. It is operated by Cairn Energy, a small British exploration company, to look for new oil deposits deep under these icy seas.

Cairn is the only company anywhere on Earth drilling new deep water exploratory wells in the frozen North this year, blazing a trail for the rest of the industry and sparking a dangerous new Arctic oil rush.

Greenpeace wanted to stop Cairn because our continuing addiction to oil is cooking the climate and because an Arctic spill would be devastating for the Greenland environment. We have seen the terrible consequences of accidents like Deepwater Horizon in the Gulf of Mexico and the Exxon Valdez spill in Alaska. An Arctic oil spill could be even worse.

Despite these risks, Cairn repeatedly refused to publish its oil spill response plan, a document that would supposedly prove how the company would deal with any accidents. It hid behind the Greenland government, the Danish Navy and various courts in a desperate attempt to keep it secret.

I climbed the Leiv Eiriksson to demand a copy of this document from the rig's captain. Unsurprisingly, he refused. We were arrested and spent the best part of two weeks in a Greenlandic prison cell.

But the campaign didn ft stop there. We were followed by others, including our Executive Director Kumi Naidoo, who climbed the rig himself. Thanks to them, and the efforts of over a hundred thousand people around the world who asked for the plan, Cairn was forced to publish it.

It's no wonder Cairn didn't want you to see this document because, by its own admission, a spill off Greenland would be impossible to clean up. See for yourself.

The plan says that any clean up operation would stop completely during the long, icy winter months; recovering oil using booms and skimmers would not be effective in freezing Arctic waters; even in ideal conditions oil recovery rates are likely to be very low; moving ice would trap spilt oil and move it miles away from the blow out to melt in the spring; clean up techniques can be so damaging that some oiled beaches would be best left to grecover naturally. The impact on Arctic wildlife would be devastating, causing major problems for narwhals and breeding colonies of puffins and razorbills.

Cairn say it will try to cut out chunks of oiled ice to melt them in heated warehouses, but it's ok as marine mammals and fish will swim out of the way of any spilled oil.

This incredible plan is wholly inadequate. Greenland should cancel Cairn's drilling programme this year and refuse future licences because we simply cannot deal with the consequences of an accident there. The Cairn plan makes this abundantly clear.

Today we are appearing in court to face charges relating to climbing the Leiv Eiriksson and I believe the evidence in Cairn's spill plan vindicates why we took peaceful direct action to stop the rig. This company should not be allowed to gamble with the unique Greenlandic environment.

The Arctic is undergoing profound change. In many ways this change is a direct result of global warming. The polar regions act like a planetary air conditioning system but at the moment the Arctic sea ice appears to be melting faster than ever before. The extent and volume of Arctic sea ice in particular is so critical because it is a litmus test for the health of our climate. Greater melting indicates more rapid climate change. And as in the past miners used a canary to warn of the presence of dangerous gases underground, today we can use the summer ice extent to warn of the dangers of climate change.

Because all the signs are there.

As the melting continues, countries like the USA and Russia are engaged in a grubby resource grab, staking a claim for the riches they think lie under the disappearing ice. This raises the prospect of industrialisation, militarisation and rising tensions amid the ice floes and glaciers of the high North.

Now the oil industry is also getting in on the act. Rather than seeing the plight of the Arctic as a spur to positive action to tackle climate change, companies like Cairn, Shell and Exxon see the melting as a business opportunity, rushing in to extract more of the fossil fuels that cause the melting in the first place.

You couldn't make it up. But perhaps what is most tragic is that even if we get all the oil that might exist under the Arctic it will only provide three years worth of the world's oil. Just three years.

The price of Arctic oil is far too high. That is why we took personal responsibility to try and stop Cairn from drilling off Greenland. And this is why our campaign will continue whatever the outcome of Friday's court case.