Question

How are the earth's principal biological systems being depleted ?

Answer 1

Climate change is happening. Its impacts and costs will be

large, serious, and unevenly spread. The impacts may be

reduced by adaptation, and moderated by mitigation,

especially by reducing emissions of greenhouse gases.

However, global efforts to reduce emissions have not yet

been suffi ciently successful to provide confi dence that the

reductions needed to avoid dangerous climate change will

be achieved. It is hoped that post-2012 emission reduction

targets will stimulate greater action through more effective

mechanisms, but there is a serious risk that suffi cient

mitigation actions will not be introduced in time, despite

the fact that the technologies required are both available

and affordable.

It is likely that global warming will exceed 2°C this century

unless global greenhouse gas emissions are cut by at least

50% of 1990 levels by 2050, and by more thereafter. There

is no credible emissions scenario under which global mean

temperature would peak and then start to decline by 2100.

Unless future efforts to reduce greenhouse gas emissions

are much more successful then they have been so far,

additional action may be required should it become

necessary to cool the Earth this century.

Such action might involve geoengineering, defi ned as the

deliberate large-scale intervention in the Earth’s climate

system, in order to moderate global warming

None of the geoengineering methods evaluated offers an

immediate solution to the problem of climate change, or

reduces the need for continued emissions reductions.

In most respects Carbon Dioxide Removal methods would

be preferable to Solar Radiation Management methods

because they effectively return the climate system to closer

to its natural state, and so involve fewer uncertainties and

risks. Of the Carbon Dioxide Removal methods assessed,

none has yet been demonstrated to be effective at an

affordable cost, with acceptable side effects. In addition,

removal of CO2 from the atmosphere only works very

slowly to reduce global temperatures (over many decades).

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