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The urgency of responding to climate change looks very different if you are a drowning island state than if you are a huge nation that stands to find its ports unfreezing in winter, its frozen wastelands becoming fertile and its abundant fossil fuel reserves more accessible.

Trade routes will follow less and less the rivers and seas; men and goods will be flown more and more directly to their goal. Countries like England and France will lose the commercial advantage of abundant coast lines conveniently indented; countries like Russia, China, and Brazil, which were hampered by the excess of their land mass over their coasts, will cancel part of that handicap by taking to the air.

As long as a pro-Russian government held sway in Kiev, the Russians could be confident that its buffer zone would remain intact and guard the North European Plain. Even a studiedly neutral Ukraine, which would promise not to join the EU or NATO and to uphold the lease Russia had on the warm-water port at Sevastopol in Crimea, would be acceptable. That Ukraine was reliant on Russia for energy also made its increasingly neutral stance acceptable, albeit irritating. But a pro-Western Ukraine with ambitions to join the two great Western alliances, and which threw into doubt Russia's access to its Black Sea port? A Ukraine that one day might even host a NATO naval base? That could not stand.

Russia does not have to send an armoured division into Latvia, Lithuania or Estonia to influence events there, but if it ever does it would justify the action by claiming that the large Russian communities there are being discriminated against. In both Estonia and Latvia approximately one in four people are ethnically Russian and in Lithuania it is 5.8 per cent. In Estonia the Russian speakers say they are under-represented in government and thousands do not have any form of citizenship. This does not mean they want to be part of Russia, but they are one of the levers Russia can pull to influence events.

This lack of a warm-water port with direct access to the oceans has always been Russia's Achilles heel, as strategically important to it as the North European Plain. Russia is at a geographical disadvantage, saved from being a much weaker power only because of its oil and gas.

The Russian-speaking populations in the Baltics can be stirred up to making life difficult. There are existing, fully formed political parties already representing many of them. Russia also controls the central heating in the homes of the Baltic people. It can set the price people pay for their heating bills each month, and, if it chooses, simply turn the heating off.

The sharp decline in population growth may have been arrested, but it remains a problem. The average lifespan for a Russian man is below sixty-five, ranking Russia in the bottom half of the world's 193 UN member states, and there are now only 144 million Russians (excluding Crimea).

Russia has never been conquered from this direction, partially due to its strategic depth. By the time an army approaches Moscow it already has unsustainably long supply lines, a mistake that Napoleon made in 1812, and that Hitler repeated in 1941.

ON 1 OCTOBER 1939, Winston Churchill made a famous speech in which he discussed the prospect of Russia joining the Second World War: 'I cannot forecast to you the action of Russia. It is a riddle wrapped in a mystery inside an enigma; but perhaps there is a key. That key is Russian national interest.'

On average, more than 25 per cent of Europe's gas and oil comes from Russia; but often the closer a country is to Moscow, the greater its dependency. This in turn reduces that country's foreign policy options. Latvia, Slovakia, Finland and Estonia are 100 per cent reliant on Russian gas, the Czech Republic, Bulgaria and Lithuania are 80 per cent dependent, and Greece, Austria and Hungary 60 per cent. About half of Germany's gas consumption comes from Russia, which, along with extensive trade deals, is partly why German politicians tend to be slower to criticise the Kremlin for aggressive behaviour than a country such as Britain, which not only has 13 per cent dependency, but also has its own gas-producing industry, including reserves of up to nine months' supply.

RUSSIA IS VAST. IT IS VASTEST. IMMENSE. IT IS SIX MILLION square miles vast, eleven time zones vast; it is the largest country in the world.

Winston Churchill's famous observation of Russia, made in 1939: 'It is a riddle wrapped in a mystery inside an enigma',