New Scientist special about what we do/don't know about Climate change

Climate change: What we do – and don’t – know – New Scientist.

(Image: Maria Stenzel)

There is much we do not understand about Earth’s climate. That is hardly surprising, given the complex interplay of physical, chemical and biological processes that determines what happens on our planet’s surface and in its atmosphere.

Despite this, we can be certain about some things. For a start, the planet is warming, and human activity is largely responsible. But how much is Earth on course to warm by? What will the global and local effects be? How will it affect our lives?Watch movie online A Cure for Wellness (2017)

In these articles, Michael Le Page sifts through the evidence to provide a brief guide to what we currently do – and don’t – know about the planet’s most burning issue.

KNOW

Greenhouse gases are warming the planet

From melting glaciers and earlier springs to advancing treelines and changing animal ranges, many lines of evidence back up what thermometers tell us
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DON’T KNOW

How high greenhouse gas levels will rise

We can’t say how much Earth will warm over the coming years unless we know how much more greenhouse gas will end up in the atmosphere
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KNOW

Other pollutants are cooling the planet

We pump all kinds of substances into the atmosphere. Some of them reflect the sun’s heat back into space and so cool things down
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DON’T KNOW

How great our cooling effects are

Pollutants that form minute droplets in the atmosphere have horrendously complex effects – so it’s far from certain what they mean for global warming
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KNOW

The planet is going to get a lot hotter

Extra carbon dioxide means a warmer world – and then positive feedback effects from things like water vapour and ice loss will make it warmer still
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DON’T KNOW

Just how much hotter things will get

On current trends the temperature rise could exceed 4 °C as early as the 2060s. But even that could be an underestimate
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DON’T KNOW

How things will change in each region

Which regions are going to turn into tropical paradises? Which into unbearably humid hellholes? It would be useful to know. Unfortunately, we don’t
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KNOW

Sea level is going to rise many metres

Studies of past climate indicate each 1 °C rise in the global mean temperature eventually leads to a 20-metre rise in sea level
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DON’T KNOW

How quickly sea level will rise

Do we have time to get temperatures back down before seas rise by more than a few metres? We have little clue how much room we have for manoeuvre
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DON’T KNOW

How serious the threat to life is

The problem for the plants, animals and people living today is that they and we have adapted to the unusually stable climate of the past few thousand years
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KNOW

There will be more floods and droughts

Warm air holds more moisture. This means more rain or snow overall, and more intense rain or snowfall on average
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DON’T KNOW

Will there be more hurricanes and the like?

A wetter atmosphere will provide more of the fuel that powers extreme events like hurricanes, but it is not clear how often this fuel will be ignited
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DON’T KNOW

If and when tipping points will come

The Amazon could become grassland. Massive amounts of methane could be released from undersea hydrates. And we may not realise in time to do anything about it
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