Climate Change: How Do We Know?
This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct
measurements, gives evidence that atmospheric CO has risen since the Industrial Revolution. (Credit: Luthi,
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D., et al.. 2008; Etheridge, D.M., et al. 2010; Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa
CO record.)
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The Earth's climate has changed throughout history. In the last 650,000
years there have been seven cycles of glacial advance and retreat, with the abrupt
end of the ice age about 7,000 years ago marking the beginning of the modern
climate era — and of human civilization. Most of these climate changes are
attributed to very small variations in Earth’s orbit that change the amount of solar
energy our planet receives.
Scientific evidence for warming of the climate system is
unambiguous.
- Intergovernmental Panel on Climate Change
The current warming tendency is particularly colossal because most of it is
extremely likely (greater than 95 percent probability) to be the result of human
activity since the mid-20th century and proceeding at a rate that is unprecedented
for millennias.
Earth-orbiting satellites and other technological advances have enabled
scientists to see the big picture, collecting many different types of data about our
planet and its climate on a global scale. This body of information, collected over
many years, unveils the changing of the climate on Earth.
The heat-trapping nature of carbon dioxide and other gases have been
demonstrated since the mid-19th century. Their aptitude to affect the transfer of
infrared energy in the atmosphere is the scientific basis of almost every
instrument flown by NASA. There is no question that increasing level of
greenhouse gases must cause the Earth to be warmer in response.
Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers
reveal that the Earth’s climate responds to changes in greenhouse gases level.
Ancient evidence can also be found in tree rings, ocean sediments, coral reefs,
and layers of sedimentary rocks. This ancient, or paleoclimate, evidence shows
that current warming is occurring roughly ten times as rapid as the average rate of
ice-age-recovery warming.
The testament for rapid climate change includes:
Rising Of Global Average Temperature
The planet's average surface temperature has
increased about 0.9 degrees Celsius since
the late 19th century, a change driven
largely by the rising amount of carbon
dioxide and other human-made emissions
into the atmosphere. Most of the warming
occurred in the past 3 decades, with the five
warmest years on record taking places since
2010. Not only was 2016 the warmest year
on record, but 8 of the 12 months of that
year — from January to September, with the
exception of June — were the warmest on
record for those respective months.
Warming Oceans
The oceans have absorbed much of this
increased heat, with the top 700 meters of
ocean showing warming for more than 0.4
degrees Fahrenheit since 1969.
Shrinking Of Ice Sheets
The Greenland and Antarctic ice
sheets have declined dramatically.
Data from NASA's Gravity
Recovery and Climate Experiment
has revealed that Greenland lost an
average of 286 billion tons of ice
every from 1993 to 2016, whereas
Antarctica lost about 127 billion tons
of ice every year during the same
period. Moreover, the rate of
Antarctica ice loss has tripled in the
last decade.
Image: Flowing meltwater from the
Greenland ice sheet
Glacial Retreat
Glaciers are retreating nearly
everywhere around the world —
including in the Alps, Himalayas,
Andes, Rockies, Alaska and Africa.
Image: The disappearing of the snowcover
of Mount Kilimanjaro, from space.
Decrease Of Snow Cover
Satellites observations unveil that
the amount of spring snow cover in
the Northern Hemisphere has
declined over the past 50 years and
that snow is melting earlier.
Rise of sea level
Global sea level increased about 8
inches in the last century. The rate in
the last 20 years, nevertheless, is
nearly double that of the last century
and is accelerating slightly every
year.
Image: Republic of Maldives: Vulnerable
to sea level rise
Declining Of Arctic Sea Ice
Both the extent and thickness of
Arctic sea ice has decreased rapidly
over the last several decades.
Image: Visualization of the 2013 Arctic
sea ice minimum, the lowest on record
Extreme Events
The number of record high
temperature events in the United
States has been increasing, whereas
that of record low temperature
events has been declining since
1950. The U.S. has also witnessed
increasing numbers of intense
rainfall events.
Ocean Acidification
Since the beginning of the Industrial
Revolution, the acidity of surface
ocean waters has rised by
approximately 30%. This increase is
the result of emitting more carbon
dioxide into the air and hence more
being absorbed into the oceans. The
amount of carbon dioxide absorbed
by the upper layer of the oceans
increases by about 2 billion tons per
year.
