Robust findings
and key uncertainties
Robust findings
Observed changes Warming is un ambiguous, as demonstrated by observations such as:
in climate, their effects
- rises in global average air and sea temperatures and average sea levels,
and their causes
- widespread melting of snow and ice;
Observed changes in many biological and physical systems are consistent with warming:
- many natural systems on all continents and oceans are affected;
70% growth of greenhouse gas emissions in terms of the global warming potential between 1970 and 2004;
Concentrations of methane (CH
4
), carbon dioxide (CO
2
) and nitrous oxide (N
2
O) are now far higher than their
natural range over many thousands of years before industrialization (1750);
Most of the warming over the last 50 years is "very likely" to have been caused by anthropogenic increases in
greenhouse gases.
Causes Global GHG emissions will continue to grow over decades unless there are new policies to reduce climate
and projections of
change and to promote sustainable development.
future climate changes Warming of about 0.2°C a decade is projected for the next two decades (several IPCC scenarios).
and their impacts
Changes this century would "very likely" be larger than in the 20
th
.
Greater warming over land than sea, and more in the high latitudes of the northern hemisphere.
The more the planet warms, the less CO
2
it can absorb naturally.
Warming and rising sea levels would continue for centuries, even if GHG emissions were reduced and
concentrations stabilized, due to feedbacks and the time-lag between cause and effect.
If GHG levels in the atmosphere double compared with pre-industrial levels, it is “very unlikely” that average
global temperatures will increase less than 1.5°C compared with that period.
Responses to Some planned adaptation to climate change is occurring, but much more is needed to reduce vulnerability.
climate change
Long term unmitigated climate change will "likely" exceed the capacity of people and the natural world to adapt.
Many technologies to mitigate climate change are already available or likely to be so by 2030. But incentives
and research are needed to improve performance and cut cost.
The economic mitigation potential, at costs from below zero to US$100 per tonne of CO
2
eq, is enough to offset
the projected growth of global emissions or to cut them to below their current levels by 2030.
Prompt mitigation can buy time to stabilize emissions and to reduce, delay or avoid impacts.
Sustainable development and appropriate policy-making in sectors not apparently linked to climate help to
stabilize emissions.
Delayed emissions reductions rincrease the risk of more severe climate change impacts.
6 Planet in Peril
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