“What we Know about Climate Change”
by P. Brian Fisher, Ph.D.
In the last 100 years, global temperature has increased 1.3F. The pace of this increase in temperature is
also accelerating. We know this from thermometer records, tree rings, and ice core samples, all of which
consistently show that the earth is warming. This is undisputed. The primary cause of this warming is
from humans. We burn fossil fuels that contribute to heat-trapping gases that thicken the greenhouse
gas layer of our atmosphere. As this layer thickens, it traps more heat from the sun, which warms the
earth. This warming then leads to changes in our climate.
The human contribution to climate changes is the area where many in the public seem to have the most
doubt, so let’s address how we know that most of this warming is from human activities.
First, the long-term climate record on climate change, going back 650,000 years, shows natural variation
in earth’s climate. This record derived from measuring heat-trapping gases like carbon that are stored in
ice. It shows six cycles (or glacial periods), each lasting approximately 100,000 years. These cycles are
uniform and consistent. These cycles oscillate between valleys based on low carbon, low temperature
and peaks with high carbon, higher temperature. Today, we are at the beginning of a period in this
natural cycle of decreasing carbon and cooling. Yet, carbon, the most prominent heat-trapping gas, is
skyrocketing and so is warming. Today, in fact, there is by far more carbon in the atmosphere than at
any point in these natural cycles.
Second, solar activity (changes in the radiation levels that reach earth) has a limited role in the warming.
While solar activity did have a slight influence on pre-industrial climate, it has had a negligible effect in
last 30 years, and in fact, current trends suggest a cooling from solar activity.
Third, the signatures or fingerprints in the atmosphere are unmistakably human. When we look at the
layers of the atmosphere we see that the atmosphere below the greenhouse gas layer is warming, while
the atmosphere above it is actually cooling. The cooling in the upper atmosphere is consistent with
natural trends, while the warming in the lower atmosphere is consistent with human-induced changes
to the heat-trapping greenhouse layer. If all the warming were from natural cycles and events, then we
would see consistent temperatures throughout all levels of earth’s atmosphere. We don’t. When we
factor human activities into the climate equation, we see a very consistent explanation for our current
increases in global temperature.
Fourth, there is a quickly growing record of observed changes to climate by those in climate sensitive
areas. This aspect cannot be underestimated because people in these communities have a long history
of adapting to natural, but much slower, variations in climate. Today, the difference is that because of
the heavy use of fossil fuels by humans, these changes to climate are occurring much faster and in ways
that these communities have never seen before. In the Arctic, Small Islands, poor coastal areas in
Bangladesh and Africa, people have documented how their climate is changing in very fundamental
ways. These communities all have in common a reliance on the environment for their daily survival. And
thus, for generations, the viability of their communities depended on the accuracy of climate
information. So, this information is reliable and critical to our understanding of what is happening. These
observations are consistent across extremely different geographic, social and cultural locations, and
they provide strong support to other climate measurements and data. In addition, it helps illuminate
what we can expect in the future in places like South Carolina.
Finally, local weather is not necessarily always consistent with climate because it’s a very short-term
variation, while climate is based on long-term changes. However, the weather experienced along the
east coast, for example the major snowstorms, is consistent with climate trends for the Eastern US. In
general, climate change works at the extreme margins. For the Eastern US, this means that we can
expect to see more extreme ends of the temperature and precipitation, with more days say above 100
degrees (than in the past), and more precipitation and intense precipitation events. Climate change does
not work by slowly increasing daily average temperature and slowly increasing average precipitation;
rather, it changes the extremes. This is one of the most important aspects of climate change, because by
changing those extremes, it increases risk and the ability to adapt to those changes. It means though,
that we will see weather more consistent with what we experienced this past winter.
So, here is what we know. The world is warming. Human activities are largely the cause. We are positive.
It will affect us all now and your kids and grandkids. And we will experience it largely through extremes,
which intensify the risks. What the risks are, how they can be managed effectively and efficiently, and
the specific challenges they present should now be the focus of our collective discussion.