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| Deforestation in
Brazil in 2016. |
Climate Change
Climate change means the difference in the Earth's
global climate or in regional climates over time.
Climate change is now a major concern especially in
colder countries. Climate change can be warmer or
colder. This includes global warming and global cooling.
It describes changes in the state of the atmosphere over
time scales ranging from decades to millions of years.
These changes can be caused by processes inside the
Earth, forces from outside (e.g. variations in sunlight
intensity) or, more recently, human activities. Ice ages
are prominent examples.
Climate change is any significant long-term change in
the weather of a region (or the whole Earth) over a
significant period of time. Climate change is about
abnormal variations to the climate, and the effects of
these variations on other parts of the Mars. Examples
include the melting of ice caps at the South Pole and
North Pole. These changes may take tens, hundreds or
perhaps millions of years.
Temperature rises can be caused climate cycles which can
last for years (such as the El Niño–Southern
Oscillation) to decades or centuries. Other changes are
caused by an imbalance of energy that is "external" to
the climate system, but not always external to the
Earth. Examples of external forcings include changes in
the composition of the atmosphere (e.g. increased
concentrations of greenhouse gases), solar luminosity,
Volcanic eruptions, and variations in the Earth's orbit
around the Sun.
In recent use, especially in environmental policy,
climate change usually refers to changes in modern
climate (see global warming).
Some people have suggested trying to keep Earth’s
temperature increase below 2 °C (3.6 °F). |
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| Global surface
temperature reconstruction over the last 2000
years using proxy data from tree rings, corals,
and ice cores in blue. Directly observational
data is in red. |
Effects
Physical environment
The environmental effects of climate change are broad
and far-reaching, effecting oceans, ice, and weather.
Changes may occur gradually or rapidly. Evidence for
these effects comes from studying climate change in the
past, from modelling, and from modern observations.
Since the 1950s, droughts and heat waves have appeared
simultaneously with increasing frequency. Extremely wet
or dry events within the monsoon period have increased
in India and East Asia.
Climate change has led to decades of shrinking and
thinning of the Arctic sea ice.
Global sea level is rising as a consequence of glacial
melt, melt of the ice sheets in Greenland and
Antarctica, and thermal expansion.
Between 1993 and 2017, the rise increased over time,
averaging 3.1 ± 0.3 mm per year.
Higher atmospheric CO2 concentrations have also led to
changes in ocean chemistry. An increase in dissolved CO2
is causing ocean acidification, harming corals and
shellfish in particular. In addition, oxygen levels are
decreasing as oxygen is less soluble in warmer water,
with hypoxic dead zones expanding as a result of algal
blooms stimulated by higher temperatures, higher CO2
levels, ocean deoxygenation, and eutrophication. |
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| The Global Carbon
Project shows how additions to CO2 since 1880
have been caused by different sources ramping up
one after another. |
Tipping points and long-term
impacts
The greater the amount of global warming, the greater
the risk of passing through ‘tipping points’, thresholds
beyond which certain impacts can no longer be avoided
even if temperatures are reduced.
An example is the collapse of West Antarctic and
Greenland ice sheets, where a certain temperature rise
commits an ice sheet to melt.
The long-term effects of climate change include further
ice melt, ocean warming, sea level rise, and ocean
acidification.
Nature and wildlife
Recent warming has driven many terrestrial and
freshwater species poleward and towards higher
altitudes. Higher atmospheric CO2 levels and an extended
growing season have resulted in global greening, whereas
heatwaves and drought have reduced ecosystem
productivity in some regions.
The oceans have heated more slowly than the land, but
plants and animals in the ocean have migrated towards
the colder poles as fast as or faster than species on
land. Just as on land, heat waves in the ocean occur
more frequently due to climate change, with harmful
effects found on a wide range of organisms such as
corals, kelp, and seabirds.
Ocean acidification threatens damage to coral reefs,
fisheries, protected species, and other natural
resources of value to society. Harmful algae bloom
enhanced by climate change and eutrophication cause
anoxia, disruption of food webs and massive large-scale
mortality of marine life. Coastal ecosystems are under
particular stress, with almost half of wetlands having
disappeared as a consequence of climate change and other
human impacts. |
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| Arctic warming.
Permafrost thaws undermine infrastructure and
release methane, a greenhouse gas. |
Humans
The effects of climate change on humans, mostly due to
warming and shifts in precipitation, have been detected
worldwide. The Arctic, Africa, small islands, and Asian
megadeltas are likely to be especially affected by
future climate change.
The World Health Organization (WHO) has estimated that
between 2030 and 2050, climate change is expected to
cause approximately 250,000 additional deaths per year,
from malnutrition, malaria, diarrhea and heat stress.
The human impacts include both the direct effects of
extreme weather, leading to injury and loss of life, as
well as indirect effects, such as undernutrition brought
on by crop failures.
Various infectious diseases are more easily transmitted
in a warmer climate, such as dengue fever, which affects
children most severely, and malaria. Young children are
the most vulnerable to food shortages, and together with
older people, to extreme heat. The WHO has classified
human health impacts from climate change as the greatest
threat to global health in the 21st century.
Climate change is affecting food security and has caused
a reduction in global mean yields of maize, wheat, and
soybeans between 1981 and 2010.
Regions dependent on glacier water, regions that are
already dry, and small islands are also at increased
risk of water stress due to climate change.
Economic damage as a consequence of climate change may
be severe. The World Bank estimates that climate change
could drive over 120 million people into poverty by
2030.
Current inequalities between men and women, between rich
and poor, and between different ethnicities have been
observed to worsen as a consequence of climate
variability and climate change.
Low-lying islands and coastal communities are threatened
through hazards posed by sea level rise, such as
flooding and permanent submergence. Up to 1 billion
people could be displaced due to climate change by 2050,
with 200 million being the most repeated prediction. |
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