Understanding Scientific Terms About Climate Change
Uncertainty is ubiquitous in our daily lives. We are uncertain
about where to go to college, when and if to get married, who will
play in the World Series, and so on.
To most of us, uncertainty means not knowing. To scientists,
however, uncertainty is how well something is known. And, therein
lies an important difference, especially when trying to understand
what is known about climate change.
In science, there's often not absolute certainty. But, research
reduces uncertainty. In many cases, theories have been tested and
analyzed and examined so thoroughly that their chance of being
wrong is infinitesimal. Other times, uncertainties linger despite
lengthy research. In those cases, scientists make it their job to
explain how well something is known. When gaps in knowledge exist,
scientists qualify the evidence to ensure others don't form
conclusions that go beyond what is known.
Even though it may seem counterintuitive, scientists like to
point out the level of uncertainty. Why? Because they want to be as
transparent as possible and it shows how well certain phenomena are
understood.
Decision makers in our society use scientific input all the
time. But they could make a critically wrong choice if the unknowns
aren't taken into account. For instance, city planners could build
a levee too low or not evacuate enough coastal communities along an
expected landfall zone of a hurricane if uncertainty is
understated. For these reasons, uncertainty plays a key role in
informing public policy.
Taking into account the many sources of scientific
understanding, climate scientists have sought to provide
decision-makers with careful language regarding uncertainty. A
"very likely" outcome, for example, is one that has a greater than
90 percent chance of occurring. Climate data or model projections
in which we have "very high confidence" have at least a 9 out of 10
chance of being correct.
However, in this culture of transparency where climate
scientists describe degrees of certainty and confidence in their
findings, climate change deniers have linked less than complete
certainty with not knowing anything. The truth is, scientists know
a great deal about climate change. We have learned, for example,
that the burning of fossil fuels and the clearing of forests
release carbon dioxide (CO2) into the atmosphere. There is no
uncertainty about this. We have learned that carbon dioxide and
other greenhouse gases in the atmosphere trap heat through the
greenhouse effect. Again, there is no uncertainty about this. Earth
is warming because these gasses are being released faster than they
can be absorbed by natural processes. It is very likely (greater
than 90 percent probability) that human activities are the main
reason for the world's temperature increase in the past 50
years.
Scientists know with very high confidence, or even greater
certainty, that:
Scientists are uncertain, however, about how much global warming
will occur in the future (between 2.1 degrees and 11 degrees
Fahrenheit by 2100). They are also uncertain how soon the summer
sea ice habitat where the ringed seal lives will disappear.
Curiously, much of this uncertainty has to do with—are you
ready?—humans. The choices we make in the next decade, or so, to
reduce emissions of heat-trapping gasses could prevent catastrophic
climate change.
So, what's the bottom line? Science has learned much about
climate change. Science tells us what is more or less likely to be
true. We know that acting now to deeply reduce heat-trapping
emissions will limit the scope and severity of further impacts –
and that is virtually certain.
Learn more about how
scientists define certainty and uncertainty.
http://www.ucsusa.org/global_warming/science_and_impacts/science/certainty-vs-uncertainty.html