What is the difference between climate change and global warming?
What is the difference between weather and climate?
Some people say “weather is what you get” and “climate is what you expect.” “Weather” refers to the more local changes
in the climate we see around us, on short timescales from minutes to hours to days to weeks. Examples are familiar – rain, snow, clouds, winds, thunderstorms,
heat waves and floods. “Climate” refers to longer-term averages (they may be regional or global), and can be thought of as the weather averaged
over several seasons, years or decades. Climate change is harder for us to get a sense of because the timescales involved are much longer, and the impact
of climate changes can be less immediate. Examples of climate change include several drier-than-normal summers, a trend of, say, winters becoming milder from
our grandparents’ childhood to our own, or variations in effects like El Niño or La Niña.
Is the sun causing global warming?
No. The sun can influence the Earth’s climate, but it isn’t responsible for the warming trend we’ve seen over the past few decades. The
sun is a giver of life; it helps keep the planet warm enough for us to survive. We know subtle changes in the Earth’s orbit around the sun are responsible
for the comings and goings of the ice ages. But the warming we’ve seen over the last few decades is too rapid to be linked to changes in Earth’s
orbit, and too large to be caused by solar activity. In fact, recently (2005-2010) the sun has become less active, while temperatures have marched upwards.
One of the “smoking guns” that tells us the sun is not causing global warming comes from looking at the amount of the sun’s energy that
hits the top of the atmosphere. Since 1978, scientists have been tracking this using sensors on satellites and what they tell us is that there has been
no upward trend in the amount of the sun’s energy reaching Earth.
A second smoking gun is that if the sun were responsible for global warming, we would expect to see warming throughout all layers of the atmosphere, from the surface all the way up to the upper atmosphere (stratosphere). But what we actually see is warming at the surface and cooling in the stratosphere. This is consistent with the warming being caused by a build-up of heat-trapping gases near the surface of the Earth, and not by the sun getting “hotter.”
Is it too late to prevent climate change?
Humans have caused major climate changes to happen already, and we have set in motion more changes still. Even if we stopped emitting greenhouse gases today,
global warming would continue to happen for at least several more decades if not centuries. That’s because it takes a while for the planet (for example,
the oceans) to respond, and because carbon dioxide – the predominant heat-trapping gas – lingers in the atmosphere for hundreds of years. There
is a time lag between what we do and when we feel it.
In the absence of major action to reduce emissions, global temperature is on track to rise by an average of 6 °C (10.8 °F), according to the latest
estimates. Some scientists argue a “global disaster” is already unfolding at the poles of the planet; the Arctic, for example, may be ice-free
in the summer within just a few years. Yet other experts are concerned about Earth passing one or more “tipping points” – abrupt, perhaps
irreversible changes that tip our climate into a new state.
But it may not be too late to avoid or limit some of the worst effects of climate change. Responding to climate change will involve a two-tier approach:
1) “mitigation” – reducing the flow of greenhouse gases into the atmosphere; and 2) “adaptation” – learning to live
with, and adapt to, the climate change that has already been set in motion. The key question is: what will our emissions of carbon dioxide and other pollutants
be in the years to come? Recycling and driving more fuel-efficient cars are examples of important behavioral change that will help, but they will not be
enough. Because climate change is a truly global, complex problem with economic, social, political and moral ramifications, the solution will require both
a globally-coordinated response (such as international policies and agreements between countries, a push to cleaner forms of energy) and local efforts
on the city- and regional-level (for example, public transport upgrades, energy efficiency improvements, sustainable city planning, etc.). It’s up
to us what happens next.
Is the ozone hole causing climate change?
Yes and no. The ozone hole is basically a man-made hole in the ozone layer above the South Pole during the southern hemisphere’s spring. The ozone layer,
which lies high up in the atmosphere, shields us from harmful ultraviolet (UV) rays that come from the sun. Unfortunately we punched a hole in it, through
the use of gases like chlorofluorocarbons (CFCs) in spray cans and refrigerants, which break down ozone molecules in the upper atmosphere.
While some of the sun’s UV rays slip through the hole, they account for less than one percent of the sun’s energy. So these UV rays cannot
explain the global warming of the planet.
What scientists have uncovered recently, however, is that the ozone hole has been affecting climate in the southern hemisphere. That’s because ozone
is also a powerful greenhouse gas, and destroying it has made the stratosphere (the second layer of the atmosphere going upwards) over the southern hemisphere
colder. The colder stratosphere has resulted in faster winds near the pole, which somewhat surprisingly can have impacts all the way to the equator, affecting
tropical circulation and rainfall at lower latitudes. The ozone hole is not causing global warming, but it is affecting atmospheric circulation.
Do scientists agree on climate change?
Yes, the vast majority of climate scientists – 97 percent – agree that humans are causing global warming and climate change. Most of the leading
science organizations around the world have issued public statements expressing this, including international and U.S. science academies, the United Nations
Intergovernmental Panel on Climate Change and a whole host of reputable scientific bodies around the world). The number of peer-reviewed scientific papers
that reject the consensus on human-caused global warming is a vanishingly small proportion of the published research. The small amount of dissent tends to
come from a few vocal scientists who are not experts in the climate field or do not understand the scientific basis of long-term climate processes.
What does NASA have to do with climate change?
When people think of NASA, they think of rovers on Mars, astronauts floating aboard the International Space Station, or probes veering out to the edge of
the solar system. They don’t necessarily link NASA with climate research and observations. But Earth is a planet too, and NASA is one of the biggest
players in the Earth science arena, with broad expertise on observing our climate, especially from the vantage point of space. Today it spends over a billion
dollars a year doing Earth science and has more than a dozen satellites in orbit around the planet watching the oceans, land, ice, atmosphere and biosphere.
In the 1970s, NASA’s planetary exploration budget fell dramatically. It was then that the agency really got into the business of studying our home
planet from orbit. It was also a time when people were beginning to realize that our climate could change relatively fast, on the scale of the human lifespan.
Today, we know that our climate is changing at an unprecedented rate and that humans are a key part of that change. NASA continues to launch new satellite
missions, and is also relying on aircraft (manned and unmanned), as well as scientists on the ground, to take vital measurements of things like snowpack
and hurricanes, augmenting the big-picture view we get from space.
NASA’s role is to make observations of our climate that can be used by the public, policymakers and to support strategic decisions. Its job is to
do rigorous science. However, the agency does not promote particular climate policies.
What is the greenhouse effect?
The greenhouse effect is the way in which heat is trapped close to the surface of the Earth by “greenhouse gases”. These heat-trapping gases can
be thought of as a blanket wrapped around the Earth, which keeps it toastier than it would be without them. Greenhouse gases include carbon dioxide, methane
and nitrous oxides.
Greenhouse gases arise naturally, and are part of the make-up of our atmosphere. Earth is sometimes called the “Goldilocks” planet –
it’s not too hot, not too cold, and the conditions are just right to allow life, including us, to flourish. Part of what makes Earth so amenable
is the naturally-arising greenhouse effect, which keeps the planet at a friendly 15 °C (59 °F) on average. But in the last century or so, humans
have been interfering with the energy balance of the planet, mainly through the burning of fossil fuels that give off additional carbon dioxide into the
air. The level of carbon dioxide in Earth’s atmosphere has been rising consistently for decades and traps extra heat near the surface of the Earth,
causing temperatures to rise.
How do we know what greenhouse gas and temperature levels were in the distant past?
Ice cores are scientists’ best source for historical climate data. Every winter, some snow coating Arctic and Antarctic ice sheets is left behind and
compressed into a layer of ice. By extracting cylinders of ice from sheets thousands of meters thick, scientists can analyze dust, ash, pollen and bubbles
of atmospheric gas trapped inside. The deepest discovered ice cores are an estimated 800,000 years old. The particles trapped inside give scientists clues
about volcanic eruptions, desert extent and forest fires. The presence of certain ions indicates past ocean activity, levels of sea ice and even the intensity
of the sun. The bubbles can be released to reveal the make-up of the ancient atmosphere, including greenhouse gas levels.
Other tools for learning about Earth’s ancient atmosphere include growth rings in trees, which keep a rough record of each growing season’s
temperature, moisture and cloudiness going back about 2,000 years. Corals also form growth rings that provide information about temperature and nutrients
in the tropical ocean.
If all of Earth's ice melts and flows into the ocean, what would happen to the planet's rotation?
The Earth rotates about its axis once a day, but it does not do so uniformly. Instead, the rate of rotation varies by up to a millisecond per day. Like a
spinning ice skater whose speed of rotation increases as the skater’s arms are brought closer to their body, the speed of the Earth’s rotation
will increase if its mass is brought closer to its axis of rotation. Conversely, the speed of the Earth’s rotation will decrease if its mass is moved
away from the rotation axis.
Melting land ice, like mountain glaciers and the Greenland and Antarctic ice sheets, will change the Earth’s rotation only if the meltwater flows
into the oceans. If the meltwater remains close to its source (by being trapped in a glacier lake, for example), then there is no net movement of mass
away from the glacier or ice sheet, and the Earth’s rotation won’t change. But if the meltwater flows into the oceans and is dispersed, then
there is a net movement of mass and the Earth’s rotation will change. For example, if the Greenland ice sheet were to completely melt and the meltwater
were to completely flow into the oceans, then global sea level would rise by about seven meters (23 feet) and the Earth would rotate more slowly, with
the length of the day becoming longer than it is today, by about two milliseconds.
Melting sea ice, such as the Arctic ice cap, does not change sea level because the ice displaces its volume and, hence, does not change the Earth’s
Ask A Climate Scientist
Is there any merit to the studies that show that historical carbon dioxide levels lag behind temperature, and don't lead them?
Will climate change drastically reduce our food production, or will it change what we produce?
Does the scientific community feel that global warming is decreasing or increasing?
Is the frequency of extreme weather events a sign that global warming is gaining pace and exceeding predictions?