Frequently Asked Questions
What is the greenhouse
The greenhouse effect helps to
maintain and regulate the temperature of our planet. Ever since
the industrial revolution began, factories, power plants and
eventually cars burnt fossil fuels such as oil and coal, releasing
huge amounts of gases such as carbon-dioxide, methane and others
into the atmosphere. These greenhouse gases trap heat near the
Earth in a naturally occurring process known as the ‘Greenhouse
Effect’. The greenhouse effect begins with the sun, and the energy
it radiates into the Earth. The Earth and the atmosphere absorb
some of this energy while the rest is radiated back into space.
Naturally occurring gases in the atmosphere trap some of this
energy and reflect it back warming the Earth. But over the last
few years, enhancement of the greenhouse effect through more
greenhouses gases is causing the temperature of the Earth to rise
What is causing greenhouse
gases to increase?
Human activity is causing
greenhouse gases to increase in the atmosphere, mainly carbon
dioxide. Carbon dioxide is released into the atmosphere through
the burning of fossil fuels such as coal, oil and natural gas.
Before the industrial revolution, the level of carbon dioxide in
the atmosphere was 280 parts per million by volume and the current
levels are greater than 380 parts per million by volume. If the
level if carbon dioxide continues to rise at the present rate,
then carbon dioxide levels are estimated to rise to anywhere
between 490 to 1260 parts per million by volume.
Are sea levels rising?
Yes. Global mean sea level
has been rising at an average rate of 1.7 mm/year (plus or minus
0.5mm) over the past 100 years, which is significantly larger than
the rate averaged over the last several thousand years. In India,
the Himalayas are retreating at three times the normal rate, from
19 meters in 1971 to 34 meters today. Arctic sea ice is also
sinking, which is causing water levels to rise at an alarming
What are its likely
consequences in the future?
Global temperatures are
anticipated to rise anywhere between 1.5°C to 3.0°C in the next 50
years. Rising sea levels could flood coastal areas around the
world. Weather patterns could change, making hurricanes more
frequent. Severe droughts would increase in warm areas and species
unable to adapt to the changing environment could face extinction.
Also, there would be devastating effects on population growth,
economic growth and the entire civilization as a whole.
So, what should we choose?
‘Economic Growth’ or the ‘World’?
Firstly, if you did not have a
world, there would be no economic growth, and secondly, a well
designed programme along with small and effective initiatives
taken by people by making some conscious amendments to the way in
which they lead their daily lives will ensure us to combat this
problem without having to hamper economic growth.
Yet, there are people who
do not believe that global warming exists.
Well, there are people who yet
believe that there was no Nazi Holocaust against the Jews.
warming or climate change: Which is it?
Two 19th-century scientists
are associated with the discovery that increasing carbon dioxide
in the atmosphere warms the entire planet: French researcher Jean
Baptiste Fourier and Swedish scientist Svante Arrhenius. Their
identification of what came to be called the greenhouse effect
(see box at right) applies to both natural and human-produced
additions of CO2.
As measurements of atmospheric
CO2 levels showed steady increases after World War II , Earth
system scientists looked for a corresponding rise in global
average temperatures, basing their studies on the physical laws
governing the greenhouse effect. By the early 1980s, climate
scientists were calling this atmospheric response global warming.
Not every place on Earth was expected to warm at the same rate,
and rising temperatures were not the only impacts anticipated. So
some researchers began talking about global climate change to
convey that the situation was more complex.
To some ears, "climate change"
sounds less ominous than "global warming," so the question of how
best to convey the seriousness of the problem continues.
Suggestions include "global heating" and "global water crisis."
What is the average global temperature
Climatologists prefer to
combine short-term weather records into long-term periods
(typically 30 years) when they analyze climate, including global
averages. Between 1961 and 1990, the annual average temperature
for the globe was around 57.2°F (14.0°C), according to the World
Meteorological Organization. According to estimates by the World
Meteorological Organization, in 2008 that the global temperature
was about 0.56°F (0.31°C) above that long-term average.
Why are global temperatures
usually expressed this way—as a departure from normal, instead of
a simple global temperature? One reason is that there are several
different techniques for coming up with a global average,
depending on how one accounts for temperatures above the
data-sparse oceans and other poorly sampled regions.
Since there is no universally
accepted definition for Earth’s average temperature, several
different groups around the world use slightly different methods
for tracking the global average over time. The important point is
that the trends that emerge from year to year and decade to decade
are remarkably similar—more so than the averages themselves. This
is why global warming is usually described in terms of anomalies
(variations above and below the average for a baseline set of
years) rather than in absolute temperature. A Web site from NASA's
Goddard Institute for Space Studies goes into more detail on the
topic of The Elusive Absolute Surface Air Temperature.
How much has the global temperature risen
in the last 100 years?
Averaged over all land and
ocean surfaces, temperatures have warmed roughly 1.33°F (0.74ºC)
over the last century, according to the Intergovernmental Panel on
Climate Change (see page 2 of the Summary for Policymakers in the
IPCC’s 2007 Synthesis Report). More than half of this
warming—about 0.72°F (0.4°C)—has occurred since 1979. Because
oceans tend to warm and cool more slowly than land areas,
continents have warmed the most (about 1.26°F or 0.7ºC since
1979), especially over the Northern Hemisphere.
The year 1998 was the warmest
on record for the contiguous United States, followed closely by
2006 and 1934, according to the National Climatic Data Center. In
2008, the U.S. saw its coolest year in more than a decade. It was
the first time since 1997 that the nation has been close to its
100-year average temperature (though 2008 was still slightly above
that norm). The United States was actually one of the least-warm
spots on Earth in 2008 when compared to local averages. The globe
as a whole had its coolest year since 2000, but the global average
for 2008 was still warmer than any year from 1880 to 1996,
according to NCDC.
There are slight differences
in global records between groups at NCDC, NASA, and the University
of East Anglia. Each group calculates global temperature year by
year, using slightly different techniques. However, analyses from
all three groups point to the decade between 1998 and 2008 as the
hottest since 1850.
This graph from NOAA shows the
annual trend in average global air temperature in degrees Celsius,
through 2008. For each year, the range of uncertainty is indicated
by the vertical bars. The blue line tracks the changes in the
trend over time. Click here or on the image to enlarge. (Image
courtesy NOAA's National Climatic Data Center.)
How much carbon dioxide (and other kinds
of greenhouse gas) is already in the atmosphere?
One of the strongest pieces of
evidence for human-induced climate change is the consistent rise
in carbon dioxide (CO2) in modern times, as measured at the Mauna
Loa Observatory in Hawaii, where CO2 has been observed since 1958.
As of December 2008, the concentration of CO2 in Earth’s
atmosphere was about 386 parts per million (ppm), with a steady
recent growth rate of about 2 ppm per year.
Because CO2 stays in the air
so long, it becomes very well mixed throughout the global
atmosphere. This makes the Mauna Loa record an excellent
indication of long-term trends.
concentrations of CO2 are about 30% higher than they were about
150 years ago at the dawn of the industrial revolution. According
to the Scripps Institution of Oceanography, ice core
reconstructions going back over 400,000 years show concentrations
of around 200 ppm during the ice ages and about 280 ppm during the
warm interglacial periods. In other words, our current CO2 levels
are higher than they've been in at least the last 400 millenia.
See the Scripps Web site for a graphic illustrating this trend.
Almost a quarter of the carbon
dioxide emitted by human activities is absorbed by land areas;
another quarter is absorbed by the ocean. The remainder stays in
the atmosphere for a century or longer.
Carbon dioxide accounts for
more than half of the human-produced enhancement to Earth’s
greenhouse effect. Among the other gases involved is methane,
which has increased dramatically over the last century. Methane
concentrations rose about 1% a year in the 1980s, but since about
2000 the concentration has leveled off, though a rise was observed
in 2007. The reasons for this slow growth in recent years are not
yet clear, although one possibility is a drop in the amount of
methane leaked from natural gas pipelines and plants. Methane
stays in the atmosphere for much less time than carbon dioxide
(around a decade) and there is much less of it, but molecule for
molecule, it is a far more powerful greenhouse gas. As of 2008,
the concentration of methane in Earth’s atmosphere was about 1786
parts per billion.
Other important greenhouse gases include nitrous oxide and
near-surface ozone. Water vapor is actually the most prevalent
greenhouse gas, but human activity has not directly increased its
concentration in the atmosphere, unlike the other chemicals above.
However, as global temperatures increase, more water vapor is
released by oceans and lakes, and this in turn helps to increase
temperatures further. This is one of many feedback loops that help
to reinforce and intensify climate change.
Hasn't the amount of carbon dioxide in
the atmosphere decreased recently?
People don’t always produce
more CO2 from one year to the next. When the global economy
weakens, emissions from human activities can actually drop
slightly for a year or two. Yet the accumulation of CO2 in the
atmosphere continues to rise, as shown in the graph above. It’s a
bit like a savings account: even if your contributions get smaller
in a tight budget year, the total in your account still goes up.
Vegetation also makes a
difference, because growing plants absorb CO2. Large-scale
atmospheric patterns such as El Niño and La Niña bring varying
amounts of flooding, drought, and fires to different regions at
different times, which affects global plant growth. Thus, the
amount of human-produced CO2 emissions absorbed by plants varies
from as little as 30% to as much as 80% from year to year. Over
the long term, just over half of the CO2 we add to the atmosphere
remains there for as long as a century or more. About 25% is
absorbed by oceans, and the rest by plants. This "balance sheet"
is known as the global carbon budget.
It’s not yet clear which
forests absorb the most CO2. Because the answer will influence
global planning and diplomatic agreements on climate, scientists
are working hard to measure how CO2 varies by latitude, altitude,
and season. One such study is HIPPO, a field project led by NCAR
and colleagues from 2009 to 2011 to take pole-to-pole measurements
aboard an airborne laboratory, the NSF/NCAR Gulfstream V jet.
Satellites such as Japan's GOSAT and others on the drawing board
at NASA will help fill in more carbon-budget details.
What does the ozone hole have to do with
There are a few connections
between the two, but they are largely separate issues.
First, it's important to know
that ozone plays two different roles in the atmosphere. At ground
level, "bad ozone" is a pollutant caused by human activities; it's
a major component of health-damaging smog. The same chemical
occurs naturally in the stratosphere, and this "good ozone" acts
as a shield, filtering out most of the ultraviolet light from the
Sun that could otherwise prove deadly to people, animals, and
The ozone hole refers to the
seasonal depletion of the ozone shield in the lower stratosphere
above Antarctica. It occurs as sunlight returns each spring,
triggering reactions that involve chlorofluorocarbons (CFCs) and
related molecules produced by industrial processes. These
reactions consume huge amounts of ozone over a few weeks' time.
Later in the season, the ozone-depleted air mixes with surrounding
air and the ozone layer over Antarctica recovers until the next
spring. Other parts of the globe have experienced much smaller
losses in stratospheric ozone.
Because of international
agreements to limit CFCs and related emissions instituted with the
Montreal Protocol, it's expected that the ozone hole will be
slowly healing over the next few decades.
The ozone hole does not
directly affect air temperatures in the troposphere, the layer of
the atmosphere closest to the surface, although changes in
circulation over Antarctica related to the ozone hole appear to be
changing surface temperature patterns over that continent. Ozone
is actually a greenhouse gas, and so are CFCs, meaning that their
presence in the troposphere contributes slightly to the heightened
greenhouse effect. The main greenhouse gas responsible for
present-day and anticipated global warming, however, is carbon
dioxide produced by burning of fossil fuels for electricity,
heating, and transportation.
Higher up, the loss of
stratospheric ozone has led to some cooling in that layer of the
atmosphere. An even larger effect comes from carbon dioxide, which
acts as a cooling agent in the stratosphere even though it warms
the atmosphere closer to ground level. This paradox occurs because
the atmosphere thins with height, changing the way carbon dioxide
molecules absorb and release heat. Together, the increase in
carbon dioxide and the loss of ozone have led to record-low
temperatures recently in the stratosphere and still higher up in
the thermosphere. Far from being a good thing, this cooling is
another sign that increasing levels of carbon dioxide are changing
our planet's climate.
Aren’t the computer models used to study
climate really simplistic?
Global climate models—the
software packages that simulate the past, present, and future of
our atmosphere—have grown in complexity and quality over the last
10 to 20 years. Yet even the earliest models of the 1960s, which
were quite crude by today’s standards, showed that a doubling of
carbon dioxide in the atmosphere could increase global temperature
by around 5°F (3°C). That projection remains close to the modern
consensus, and temperatures over the last 30 years have risen at a
rate consistent with this early estimate.
Far more information is
available from today’s models, such as the NCAR-based Community
Climate System Model, because they now include many more aspects
of the Earth system, including ice sheets, vegetation, cloud
areas, and soil moisture.
Research conducted for the
2007 IPCC Working Group 1 assessment compared the output from
major models at research centers around the world. While these
models are far from perfect, scientists are confident that they
capture the key processes that drive climate. For example, models
now replicate the ups and downs of 20th-century global temperature
As in other areas of science,
rigorous testing and continual improvement are part and parcel of
climate modeling. Researchers can test models against reality,
identify and correct flaws, and compare their models with others.
scientists warning us about global cooling a few years ago?
After rising in the early 20th
century, global surface temperatures cooled slightly from just
after World War II (the mid-1940s) into the 1970s.
Scientists already knew that
carbon dioxide was accumulating in the atmosphere and that it
could lead to eventual global warming. In 1975, Wallace Broecker
(Lamont-Doherty Earth Observatory) published the first major study
with "global warming" in the title.
But a few researchers believed
that pollution from burgeoning postwar industry was shielding
sunlight and shading the planet, causing the observed cooldown.
Some even theorized that a "snow blitz" could accelerate the
cooling and bring on the next ice age. Their statements got major
play in the media.
Starting in the 1970s, new
clean-air laws began to reduce sulfates and other
sunlight-blocking pollutants from U.S. and European sources, while
greenhouse gases continued to accumulate unchecked. Global
temperatures began to warm sharply in the 1980s and have continued
rising since then.
Increasingly detailed models
suggest that the more recent warmup can be attributed to
greenhouse gases overpowering the effect of sunlight-shielding
pollution. Computer simulations also suggest that today's
atmosphere would be even warmer still, were it not for that air