Scientists are warning that Siberia could be a far larger source of greenhouse gases than we had ever thought.
Follow my progress as I investigate this distant front-line in climate change.
12 SEPTEMBER: YOUR CLIMATE CHANGE QUESTIONS ANSWERED
Q: David, have you had the opportunity to ask the locals what they have noticed, and what they think about the increased temperatures and melting?
Kevin Zeller, Saint Louis, USA
Riverbanks allow a good view of the permafrost under much of Siberia
I have had the chance, and the impact of the warming is becoming very noticeable to local people. In the regional capital, Yakutsk, I saw huge holes torn in major roads where the permafrost had melted.
I also saw an urgent effort to shore up a large office block in danger of collapse. Many other buildings have not been saved.
Curiously the people of Siberia have come to rely on the extreme winter cold. For example, the freezing of the rivers opens up transport routes. The recent warming and the prospect of that accelerating are serious challenges here.
Q: As the atmosphere warms, will we not see more and more rain in some places on this planet? As a result, won't more vegetation grow and will act as a balance because more green plants will absorb more CO2?
Nish, Washington DC, USA
Climate models predict that some areas will indeed receive more rain and that in some cases plant growth will benefit. But on balance, most studies point the other way. The rainfall may fall so heavily that it causes damage, or at the wrong times of the year.
Q: Have you seen any indication of the water level rising as you have been investigating the thawing of the permafrost?
Kirk Larsen, Ledyard, USA
Yes, Sergei Zimov, the director of the Northeast Science Station here at Cherskii, Siberia, tells me that he has observed a rise in water levels.
Ironically, the prestigious Permafrost Institute in Yakutsk suffered a major flood recently.
Studies show that the melting permafrost will increase the flows of the mighty Arctic rivers and that will have an impact on sea levels worldwide - not as much as the melting of ice sheets and major glaciers but significant nonetheless.
Q: Why is there not more focus on preserving tropical forests as a global warming countermeasure? After all, most studies suggest that this is a relatively inexpensive option that also has the added benefit of preserving biodiversity.
Kjetil Aasen, Oslo, Norway
It is a very relevant question because there are discussions about precisely this idea. I reported from the Amazon rainforest last month, and Brazilian officials were actively seeking international support and finance for the conservation of the forest.
Some experts hope that a mechanism may be found within the Kyoto Treaty. But, as I write this from Siberia, I am not as up to date on this as I should be.
11 SEPTEMBER: DARK PAST OF A SIBERIAN OUTPOST
We have got our passports back from the security service. They had taken them from us when we arrived on Friday.
It's a curious reminder of the unusual nature of this region.
In Cold War days it was closed to foreigners, and even now visitors like us need a permit to get in. Alaska is only a few hours' flight away and borders evidently remain a touchy subject, however friendly the neighbours are.
During breakfast, we hear more about the dark past of this area.
Armoured personnel carriers make light work of the terrain
The rivers that we ourselves have travelled on were once used to transport prisoners to the Gulags. Some of the camps were on the coast of the Arctic Sea, about 80 miles (129 km) to the north, others were further south in the gold-mining region.
A lake that the scientists here have been studying recently - measuring emissions of greenhouse gases to assess the impact on climate change - was apparently once the scene of terrible brutality in the 1940s: a massacre of escaped inmates.
There is no trace of any of this now, but the remoteness of Cherskii is still a talking point. The capital is eight hours behind; internet access is by phone, and painfully slow.
Only a few ships make it here in the brief months when the ice breaks up. Flights are incredibly expensive and, with the runway out of action, the town has run out of its last stores of potatoes.
But the isolation encourages independence. Much of the excellent food we have eaten has been grown here on the science station - herbs, vegetables and fruit. Best of all was the roast moose.
Whatever Siberia was like in the past, we have rarely been so warm and well-fed.
10 SEPTEMBER: CURSE OF THE SIBERIAN MOZZIE
Another first: caviar for breakfast, two big bowls of the stuff from local fish - no better start to the day.
Just as well, because once we're outside we make an amazing scientific discovery: that the insects of the Amazon jungle are amateurs compared with the mosquitoes, flies and gnats of a Siberian summer.
Caviar: an ideal way to start the day
They don't last long but these Arctic antagonisers pack a lot of attitude into their brief lives.
No ear, mouth, nostril or eyeball is safe from them. Filming beside a lake turns into an aerobic session of desperate arm-waving.
Running would help but isn't possible while the ground is like marshland. Never mind what global warming might mean for the Arctic permafrost or glaciers: just imagine the boom-time it could bring for the insects.
And we're here at the tail-end of summer, when the buzzing onslaught is meant to be slackening.
We learn with particular interest how the first snows of insect-killing winter may be only a fortnight away. The only respite comes when our boat picks up speed and the wind saves us.
Logs in the water make for an exciting ride
Today's journey involves an exhilarating ride along a maze of narrow rivers. Our host, Sergei Zimov, weaving a high-speed roller-coaster path, lurches round bends and swerves past logs that have drifted out from the banks.
In a couple of months, when the waters freeze solid, he'll be driving on the river instead, and much happier.
It's hard to believe with temperatures soon to drop to minus 50, but he says the cold makes life easier.
I now know what he means. He needn't constantly swat the back of his neck. And after today, that's enough to make a Siberian winter seem appealing.
09 SEPTEMBER: MOOSEFEED AND MAMMOTH POO
It's so quiet I wake up wondering what's wrong. From my window the dawn casts a grey light over the river below us.
Cameraman Duncan Stone and I are staying in the guest house of what's called the North East Science Station, which must rank as the cosiest research institution in the world.
It's run by a highly energetic scientist, Sergei Zimov. His wife Galya, also a scientist, cooks us breakfast - a delicious mound of sweetened Yorkshire Puddings, eaten with homemade jam - before going off to feed the moose and tend her vegetable garden; it's that kind of place.
We venture out by boat, Sergei at the helm. A three-hour journey up the Kolyma river takes us to the forbidding cliffs of Duvanny Yar. Steep walls of mud and ice provide a unique cutaway view of the permafrost inside.
Sergei Zimov prefers the winter
We clamber on shore, our BBC-issue Arctic boots accumulating mud as we go.
Some patches of this terrain are firm but others are like thick soup. Eventually we learn the local technique of never lingering too long in one place and instead hopping fast like a goat to avoiding getting stuck.
I say "eventually" because I do get stuck - and frantically work to yank my boots clear.
Minutes later Duncan encounters mud sitting atop a layer of ice and finds himself sliding lens first into the gloop. It doesn't help to learn that much of this ancient mud was actually deposited there thousands of years ago by long-extinct woolly mammoths, though how many can boast that they've ever been knee deep in mammoth poo?
08 SEPTEMBER: ON THE CLIMATE FRONTLINE
Dawn at Yakutsk airport check-in never promised to be fun - the air acrid with smoke, the jostling crowds, the Soviet-era lack of clarity about small details like whether our flight was actually going to leave.
But eventually, in a plane packed with Yakut horse dealers, we climb into the Siberian sky, the drone of the propellers settling into a rhythm as we begin a 1,000-mile journey north.
A break in the clouds reveals the blue sweeps of the Kolyma river, meandering towards the Arctic Ocean. It looks stunning
One break in the clouds reveals a range of utterly bare mountains, another the blue sweeps of the Kolyma river, meandering towards the Arctic Ocean. It looks stunning.
But this is a region with a terrible history; the worst of the Gulag prison camps were here along the river banks, and I strain for a glimpse of what's left of them.
We land at a little town called Sredno-Kolymsk. It's seen better times. The main airport building has no plumbing. We watch the tea-lady empty buckets of dirty water into the mud beside the entrance.
I feel we're on a frontline that's been abandoned.
We have to wait six hours for our connection - any longer might feel like exile.
Traces of Stalin-era gulags are still visible on the Siberian landscape
The runway at our destination, the next town upriver, Cherskii, is out of action so we are ferried by helicopter, one of those enormous Russian ones which can carry dozens of people and mounds of luggage.
It flies us over an unending landscape of lakes and grassland. From the air you'd never guess we're in the Arctic - it all looks so green. But just below the surface the ground is rock solid, or at least it's meant to be - warming temperatures have started a giant thaw.
We arrive at Cherskii at twilight. It's four days since we left London; lucky it was so quick, we're told.
07 SEPTEMBER: ROOT OF THE PROBLEM
Never mind the usual measures of a country's status like the power of its economy or the size of its population. Russia wins hands down on time zones - and right now I have the feeling that they are all ganging up on me.
I crossed no fewer than six of them last night and that was just on a domestic flight from Moscow. I didn't sleep a wink as we raced towards dawn and the remote city of Yakutsk.
This tusk belongs to an extinct inhabitant of Siberia - the mammoth
Look on a map of Russia's north-east and Yakutsk is one of the little dots that look like oases in a desert of unimaginable size. A brisk chill bears a hint of the winter to come.
Temperatures here vary every year by a staggering 100C (180F) and now we're somewhere near the middle. Except that we venture into one of Yakutsk's most famous attractions, the Permafrost Institute, and find ourselves shivering in -5C (23F).
Permafrost is frozen soil and the institute's main lab is actually deep underground in the midst of it. Stepping down into it is like walking into a darkened freezer. I feel a bit light-headed and wonder if it's the clammy air or the time zones catching up with me.
Or there is another explanation: friends of friends had earlier suggested we join them for a light snack at lunchtime.
"Darkened freezer" - inside the Permafrost Institute in Yakutsk
It turned out to be a feast of local Yakut delicacies - cream cheese with wild strawberries, broth with wild onion and a kind of blood sausage.
But feasts naturally demand toasts and toasts in this part of the world cannot be refused.
Cameraman Duncan Stone and I shook our heads in disbelief as our glasses were filled, and then filled again, and then possibly once more. It's a bit like trying to count time zones. And tomorrow, as we head even further east and up inside the Arctic Circle, we'll cross two more.