Climate Change 2007 Update
4. What impacts of climate change have already been observed?
Glaciers are melting in many places worldwide.
In all regions of the world observations show that many
natural systems are being affected by regional
particularly by temperature increases.
Snow and ice are melting and frozen ground is thawing. The
number of glacial lakes is increasing and so is ground
instability in permafrost
regions. The flow of rivers that are fed by melting snow and
glaciers has increased, and
the temperature of lakes and rivers has risen. Spring events
such as migrations are starting earlier and the geographical
spread of species is
extending towards the poles. In addition, the
emitted by human activities has caused an increase of ocean
acidity, with poorly
understood but potentially important negative impacts.
Evidence accumulated over the past five years indicates that
changes in many physical and biological systems are linked to
the warming caused by human activities.
- Most of the warming observed since 1950 is very likely
due to the increase of
generated by human activities.
- In most cases, when long term measurements revealed
significant environmental change, the change went in the
direction that would be expected as a result of a warming
- Regions with significant changes are also the ones
experiencing significant warming.
- Model projections have linked the changes in some
physical and biological systems to the warming induced by
Despite limitations and gaps in knowledge, there is sufficient
evidence to conclude with high confidence that over the last
three decades the warming induced by human activities has had a
measurable impact on many physical and biological
Some impacts of regional
climate change are only
emerging at this stage. They remain difficult to discern because
they also depend on factors other than climate or because some
adaptation has taken place.
Temperature increases could for instance already have affected
agricultural and forest management, the number of heat related
deaths, the spread of vectors of disease such as insects
Recent changes are beginning to have effects, for instance
mountain settlements are at risk of floods due to melting
glaciers, the growing
season in the Sahelian region of Africa is shortening, and
damage from coastal flooding is increasing.