17
Are climate changes of a few degrees
a cause for concern?
Yes. Even
though an increase of a few degrees in global average temperature does not
sound like much, global average temperature during the last ice age was only
about 4 to 5 °C (7 to 9 °F) colder than now. Global warming of just a few
degrees will be associated with widespread changes in regional and local
temperature and precipitation as well as with increases in some types of
extreme weather events. These and other changes (such as sea level rise and
storm surge) will have serious impacts on human societies and the natural
world.
Both theory
and direct observations have confirmed that global warming is associated with
greater warming over land than oceans, moistening of the atmosphere, shifts in
regional precipitation patterns, increases in extreme weather events, ocean
acidification, melting glaciers, and rising sea levels (which increases the
risk of coastal inundation and storm surge). Already, record high temperatures
are on average significantly outpacing record low temperatures, wet areas are
becoming wetter as dry areas are becoming drier, heavy rainstorms have become
heavier, and snowpacks (an important source of freshwater for many regions) are
decreasing.
These
impacts are expected to increase with greater warming and will threaten food
production, freshwater supplies, coastal infrastructure, and especially the
welfare of the huge population currently living in low-lying areas. Even though
certain regions may realise some local benefit from the warming, the long-term
consequences overall will be disruptive.
It is not
only an increase of a few degrees in global average temperature that is cause
for concern—the pace at which this warming occurs is also important. Rapid
human-caused climate changes mean that less time is available to allow for
adaptation measures to be put in place or for ecosystems to adapt, posing
greater risks in areas vulnerable to more intense extreme weather events and
rising sea levels.
18
What are scientists doing to address
key uncertainties in our understanding of the climate system?
Science is a
continual process of observation, understanding, modelling, testing, and
prediction. The prediction of a long-term trend in global warming from
increasing greenhouse gases is robust and has been confirmed by a growing body
of evidence. Nevertheless, understanding of certain aspects of climate change
remains incomplete. Examples include natural climate variations on
decadal-to-centennial timescales and regional-to-local spatial scales and cloud
responses to climate change, which are all areas of active research.
Comparisons
of model predictions with observations identify what is well-understood and, at
the same time, reveal uncertainties or gaps in our understanding. This helps to
set priorities for new research. Vigilant monitoring of the entire climate
system—the atmosphere, oceans, land, and ice—is therefore critical, as the
climate system may be full of surprises.
Together,
field and laboratory data and theoretical understanding are used to advance models
of Earth’s climate system and to improve representation of key processes in
them, especially those associated with clouds, aerosols, and transport of heat
into the oceans. This is critical for accurately simulating climate change and
associated changes in severe weather, especially at the regional and local
scales important for policy decisions.
Simulating
how clouds will change with warming and in turn may affect warming remains one
of the major challenges for global climate models, in part because different
cloud types have different impacts on climate, and the many cloud processes
occur on scales smaller than most current models can resolve. Greater computer
power is already allowing for some of these processes to be resolved in the new
generation of models.
Dozens of
groups and research institutions work on climate models, and scientists are now
able to analyse results from essentially all of the world’s major Earth-System
Models and compare them with each other and with observations. Such opportunities
are of tremendous benefit in bringing out the strengths and weaknesses of
various models and diagnosing the causes of differences among models, so that
research can focus on the relevant processes. Differences among models allow
estimates to be made of the uncertainties in projections of future climate
change. Additionally, large archives of results from many different models help
scientists to identify aspects of climate change projections that are robust
and that can be interpreted in terms of known physical mechanisms.
Studying how
climate responded to major changes in the past is another way of checking that
we understand how different processes work and that models are capable of
performing reliably under a wide range of conditions.
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