The specks on ice are explorers Lonnie Dupre and Eric Larsen, setting off on the first ever unsupported summer crossing of the Arctic Ocean in order to draw attention to global warming.
Although the idea that mankind could influence Earth's global
temperature was proposed over a century ago, it wasn't until
relatively recently that scientists were able to confirm this with
confidence. Data had to be gathered from around the world,
technology had to develop to allow us to analyse that data, and
basic advances in physics and other disciplines had to come about
before we could understand it. What we now know about the climate
is thanks to literally generations of dedicated researchers.
However, it is also easier to observe climate change caused by
humans today because we've put so much more carbon dioxide into the
climate system over the past century that the impacts of climate
change are now clearly visible, affecting people and ecosystems all
over the world. More cars, more factories, and more power plantsl
are changing the climate faster than was previously possible and
causing more obvious changes.
Taking the planet's temperature
To get an accurate picture of how warm the Earth is, you need
measurements from all over because the whole planet does not heat
up at the same rate. In fact, some parts might even cool down while
the world as a whole heats up. Also, many temperature readings are
needed over time to develop an accurate long-term picture. In order
to develop a history if global temperatures, researchers have had
to travel to the farthest corners of the Earth, and come up with
ways to "go back in time".
Some sources of past temperature data:
- Historical records - Includes sources like ship's logs,
farmers' diaries and newspaper articles. When carefully evaluated,
these can provide both quantitative and qualitative data.
- Personal accounts and oral histories - Useful information can
be gathered especially from the older generations of indigenous
people who have always relied on nature for their survival, and so
are particularly observant of changes over the past decades.
- Direct (e.g. thermometer) measurements - Only go back around
300 years, and are very sparse until about 150 years ago. Also,
differences in thermometer types and other variables have to be
taken into account.
- Data collected by balloon and satellite - very useful, but only
available since 1979.
- Tree ring thickness - Width and density varies depending on
growing conditions.
- Ocean and lake sediments - Billions of tonnes of sediments
accumulate each year. The tiny preserved fossils and chemicals in
layers of sediment can be used interpret past climate.
- Coral skeletons - The water temperature that the coral grew in
can be determined from trace metals, oxygen and the isotopes of
oxygen contained in its skeleton.
- Fossil pollen - Each plant has uniquely shaped pollen. Knowing
what plants were growing at a particular time in the fossil record
lets scientists make inferences about what the climate was like at
the time.
- Ice cores - Over the centuries, snow falling on high mountains
and the polar ice caps packs down and became solid ice. Dust and
air bubbles trapped in this ice provide valuable climate data. For
example, the air trapped in the ice serves as a record of carbon
dioxide concentrations across the millennia.
- Observed melting - Rates of glacial retreat, permafrost thaw,
shrinking polar ice caps and reduction in Arctic sea ice are
indicators of both short and long term climate change.
The important thing is not to look at any one source of data
independently but instead to take them together. This produces a
scientifically compelling picture of a warming world that matches
with the corresponding increase in greenhouse gasses.
Predicting the climate future
Global climate models are mathematical representations of the
real world's climate. Some models are attempts by scientists to
boil the complex behaviour of the climate down to (comparatively!)
simple formulas in an attempt to understand the forces at work.
However, when people talk about specific predictions of long-term
climate conditions, they are usually talking about general
circulation models. In these models, the equations are tweaked
(within reason) until the model is able to predict past and present
conditions as accurately as possible when tested against actual
observations of past and present conditions.
Since it's impossible to know every last variable, and because
the model will never match the real world perfectly, scientists
compensate by running each model over and over, while making tiny
changes to the starting conditions (increasing the wind speed over
Detroit by one percent, for example) and other factors. This way
they can get an idea of the different possible outcomes. If one
result occurs more frequently than another, then it's the more
likely outcome.
In the end, each model predicts a range of possible outcomes.
For example, the IPCC, taking into account all of the different
available models, settled on a projected global temperature rise of
1.4 - 5.8° Celsius (about 3 to 8° Fahrenheit). No one can say
exactly how much the temperature will increase over the next
hundred years, but with a couple of caveats it is a safe bet that
it will be within this range.
The caveats
One thing climate models can not predict are all the possible
effects of feedback mechanisms, which might help stabilise the
climate or cause the climate to change much faster and in
unpredictable ways. Of course, it would be irresponsible to ignore
the climate models and hope for the best because of these
uncertainties. See our feedback effects page for more
information.
Another thing these models can not really predict is human
behaviour and ingenuity. We could burn more fossil fuels than
expected and end up with a hotter planet than even the worst case
scenario. Or we could deploy solutions such as renewable energy and
energy efficiency faster than thought possible, thereby eliminating
the likelihood of the higher temperatures.
US
National Oceanic and Atmospheric Administration - Climate proxy
data
American
Institute of Physics - History of climate change research
The
Climate Change Connection - Climate research
ClimatePrediction.Net - Distributed computing climate modelling
project (join the Greenpeace team on the project!)