Key uncertainties
Limited climate data coverage in some regions. Observed changes
Analysing and monitoring changes in extreme events, for example droughts, tropical cyclones, extreme
in climate, their effects
temperatures and intense precipitation (rain, sleet and snow), is harder than identifying climatic averages, and their causes
because longer and more detailed records are needed.
Difficult to determine the effects of climate change on people and some natural systems, because they may
adapt to the changes and because other unconnected causes may be exerting an influence.
Hard to be sure, at scales smaller than an entire continent, whether natural or human causes are influencing
temperatures because (for example) pollution and changes in land use may be responsible.
There is still uncertainty about the scale of CO
2
emissions due to changes in landuse, and the scale of methane
emissions from individual sources.

It is uncertain how much warming will result in the long term from any particular level of GHG concentrations, Causes
and therefore,
and projections of
it is uncertain what level - and pace - of emissions cuts will be needed to ensure a specific level of GHG future climate changes
concentrations.
and their impacts
Estimates vary widely for the impacts of aerosols and the strength of feedbacks, particularly clouds, heat
absorption by the oceans, and the carbon cycle.
Possible future changes in the Greenland and Antarctic ice sheets are a major source of uncertainty about
rising sea levels
Projections of climate change impacts beyond about 2050 are heavily
dependent on scenarios and models.
Limited understanding of how development planners factor climate into their decisions. Responses to
Effective adaptation steps are highly specific to different political, financial and geographical circumstances,
climate change
making it hard to appreciate their limitations and costs.
Estimating mitigation costs and potentials depends on assumptions about future socio-economic growth,
technological change and consumption patterns.
Not enough is known about how policies unrelated to climate will affect emissions.
Robust findings and key uncertainties 7
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