杏吧原创

IF YOU were to go out in the street and ask people what the North Pole is
like, most would probably tell you that it is very cold and very difficult to
get to, unless you like hauling sledges across vast sheets of ice while worrying
about attacks by polar bears. A few might also say that you鈥檇 see penguins on
the way, but they simply have their poles crossed.

What, till now, you could have been sure of is that no one would tell you
that at the North Pole you should expect to see an expanse of ordinary looking
open ocean with a distant view of ice floes. But according to scientists who
recently took a trip there aboard a Russian icebreaker that is exactly the view
that greeted them.

The world鈥檚 press has latched onto the story with excitement. And quite right
too. What more potent symbol of the effects of global warming could there
possibly be? The North Pole has simply turned into water and has doubtless left
a very confused Santa Claus.

It鈥檚 not the only odd event to be noticed recently. The 1990s saw seven out
of the ten warmest years since records began 150 years ago. The story is the
same if you dig deeper into ancient Chinese records, which in some places go
back 2000 years, or if you examine data from tree rings and ice cores. We appear
to be in the warmest period for a couple of millennia.

So human activity really is causing global warming, and catastrophe is
imminent? The suspicions grow stronger every day. Yet we still can鈥檛 be
absolutely certain. Even the most sophisticated climate models can鈥檛 yet deal
with all the variables and feedback loops in the atmosphere and its interaction
with sea, land and living creatures. We can鈥檛 predict exactly how the climate
might change as we add more greenhouse gases to it, nor how quickly. As
temperature rises, for example, more water will evaporate from the Earth鈥檚
surface. Water vapour in the atmosphere can add strongly to the greenhouse
effect but we don鈥檛 know by how much. Some feedback loops are quite unexpected.
Bacteria that live in clouds can seed rainstorms
(see p 4) and their numbers are
likely to be affected by warming. But exactly how, nobody knows.

We can gain a little more certainty about the future from long-term studies
of the past. The amount of carbon dioxide in the atmosphere has varied greatly
and so has the Earth鈥檚 temperature. One brilliant study was published in
Nature two weeks ago and reported earlier in New 杏吧原创
(22 April, p 28).
Luckily, the chemical composition of the shells of some types of
plankton depends upon the pH of the sea. That in turn depends on the
amount of CO₂ dissolved in the water, which in turn depends on the
concentration of CO₂ in the atmosphere. So by taking samples of ancient
sediments containing the right plankton from the sea bed we can create a
complete record of CO₂ levels for the past 60 million years.

The results aren鈥檛 encouraging. CO₂ levels emerge as the most
important factor in predicting temperature levels, which is bad news because
they are now the highest they have been for 20 million years. Levels are well on
the way to those found in the Eocene, when the world was ice-free even at the
poles and England was a steaming mangrove forest.

Uncertainties there may be. But surely there are just too many suspicious
signs for us not to do our utmost to stop CO₂ levels rising further. In
theory, governments the world over agree that effective precautionary action is
needed now. But will the action work? As we report on p 18, there are worrying
signs that major parts of the protocol negotiated in Kyoto to curb global
warming may be totally unworkable.

The protocol allows nations to sop up CO₂ from the
atmosphere鈥攂y planting forests and changing land use鈥攁s well as by
reducing CO₂ emissions. The two can be traded to reach overall targets
for CO₂ reduction. It鈥檚 a great idea but it may contain a fatal flaw:
no one really knows how to measure the CO₂ uptake of forests and lands,
nor what happens to the carbon over quite short periods of time as forests grow
and die. And because the system is complicated, it is very easy to cheat.

If we don鈥檛 want to risk more strange surprises at the North Pole we need to
focus on what really works. That means going back to putting the emphasis on
reducing CO₂ emissions as the safest way to halt global warming. It may
be a diplomat鈥檚 nightmare but the planet seems to be sending us a message.