Tundra reclamation

The risk of reglaciation - and the crippling effect of the ice age on the huge northern hemisphere landmass - mean that we should seriously consider an attempt to put an end the current ice age.

The speed of the warming

Another factor is whether the change is likely to be gradual or catastrophic.

If the flip from an ice age climate back to a more normal one is catastrophic, then it may be difficult for humans to control - since it will most-likely be governed primarily by the inertia of melting ice, and by other natural processes. In that case, what humans may be able to influence is how long it takes before the planet reaches the climate "tipping point" that signals the end of the current ice age - assuming such a "tipping point" is still in the future. After such a "tipping point" has been reached, the climate would be in "free fall" for a while - until it reaches its new stable point - and attempts to influence it during that phase would be unlikley to have very much effect.

It has been argued (e.g. by James Lovelock) that positive feedback effects from melting ice decreasing the albedo will cause the climate to go into free fall - with global temperatures increasing suddenly before they stabilise at a new level. Lovelock also claims that extinction events will compromise the biosphere's ability to absorb the shock.

I regard this scenario as unlikely. It is important to understand that the positive feedback effects from melting ice decreasing the albedo have mostly already happened. The positive feedback flip from a glacial stage to an inter-glacial warm period is practically over. Most of the ice sheets have already vanished. The effects of decreases in albedo from melting ice over the poles are now approximately balanced by negative feedback - which arises from increases in temperature producing increasing cloud cover.

There are other possible causes of positive feedback that may result in chaos-theory-style flips - but the ice-albedo effect is really the big one.

A more sensible model has the ice age climate as the base line, and pictures humanity battling against reglaciation and attempting to raise the temperature. Each degree of temperature rise is hard won - and if the interventions are halted, the planet tends to subside back to its ice-ace rest state, due to the adverse positions of the continents.

Since change is more likely to be gradual than catastrophic, that leaves humans largely in control of how fast the changes will be - and perhaps when they start.

Delaying the end of the ice age might seem attractive to some - in order to give us time to prepare for it. However, humans like living at the water's edge: they are drawn there by docks, trade, fishing, and other forces. The longer we delay planetary warming, the more infrastructure will get constructed on the existing coastlines - in the "wrong" place - and the more costly the eventual inevitable damage will be. Technology will have advanced by the time the move is due, but probably not by enough to undo the damage of constructing all the infrastructure in the wrong place.

The best thing to do is to plunge in at the earliest opportuninty - while our investment in maintaining the life-hostile and inherently-unstable ice age climate is still relatively small.

As for the rate of the changes, they will inevitably be extremely slow. The Greenland ice sheet has huge inertia - it will take a thousand years to melt it.

The Antarctic looks even more unshiftable: ice five miles thick and temperatures 37 degrees below zero down at the pole.

This is not good. If it takes 1,000 years to melt Greenland, that's 1,000 years of inconvenience and shifting coastlines. But we can hardly leave Greenland iced up. It's freezing up a whole continent - and it may drag us back into a glacial cycle again. I think we should strive to get the changes over as soon as possible. The naturally-slow rate of change caused by the thermal inertia of the huge, thick ice sheets will mean the costs associated with too-radid change will be minimal.

The risk of reglaciation, and the damage associated with being in an ice age imply that steps away from the reglaciation "cliff edge" should be taken as rapidly as reasonably possible.

Since steps to warm up the planet need to be taken, Tundra reclamation looks like one promising approach.

Interventions

• Trees

  One of the most obvious interventions associated with Tundra reclamation involves the planting of trees at high lattitudes.

  The effect of trees on albedo in black and white

  If evergreen forests can be created in the north, their dark green leaves will absorb more light - and by shrugging off snow, they will help prevent sunlight from being reflected back into space.

  Trees have local effects on temperature - by reducing albedo and degrading sunlight into heat.

  They also have larger-scale effects on temperature - by temporarily taking some carbon out of circulation - and by emitting water vapor, and some methane.

  The effect of northerly trees on temperature via reduced albedo typically outweighs any negative effects of trees as temporary carbon sinks.

  Humans can make a difference in this area with relatively low expense.

  They can select the most suitable species, raise them in nurseries, plant them out with insulating tree guards, and ensure they are properly established.

  In some areas, even the ultra-low-cost intervention of sprinkling seeds of an appropriate type on the ground may have a significant positive effect.

  Forests are successfully farmed at lower lattitudes. However, nearer the pole such activity would probably need subsidising for it to be viable.

  The effect would be local improvements in the habitat - including local warming effects.

  Possibly the use of other plants may be explored in habitats and regions where trees cannot grow.

  The effect of trees on albedo

• Black ground sheets

  The dramatic effect of a layer of black soot on temperatures in the Arctic earlier this century also suggests that black ground sheets may be an effective intervention.

  These would need to be deployed in areas where they do not spend much of their time buried by snow - or they would not be very effective.

  The idea would be to deploy black ground sheets in areas where there is snow and ice - and then once that has melted and the ground is exposed, plant trees in that area through the ground sheets.

The Antarctic

Plant aquaculture in the surrounding ocean may eventually have an impact on it.

I think efforts should probably be concentrated on the northern hemisphere for the moment, where there is more land, and a greater chance of success.

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