In 1988, Dr. James Hansen,
then Director of NASA's Goddard Institute for Space Studies, stood before the U.S.
Senate and testified that...
Global warming has reached a level such that we can ascribe
with a high degree of confidence, a cause and effect relationship
between the greenhouse effect and observed warming....
It is already happening now.
This last year, 2021,
comes in as the sixth warmest year on record,
and it continues this large
long-term warming that Jim Henson
was detecting even in 1988.
and in 1988, that was also a globally warmest year.
But now that ranks only 28th in the in the ranking.
And so the warming that we've had since
Jim Hansen's testimony has been dramatic and totally vindicates
that concern and the warnings that he put out at that time.
The Goddard Institute for Space Studies, or GISS
for short, maintains NASA's record of Earth's surface temperature,
called GISTEMP, that shows a clear and unequivocal
increase in our planet's temperature.
GISTEMP stretches from 1880,
long before NASA's existed, until the present day.
Now, when you think of NASA, you
probably think of, well, space, right?
And we do lots of work studying Earth from above.
but the GISTEMP record is actually built from the ground up
We collect measurements
taken from weather stations, Antarctic research stations.
And ships and ocean buoys all around the planet to understand
what temperature changes look like globally.
And why does the record start in 1880?
That's the earliest period that we have sufficiently reliable
measurements from ships and weather stations
in enough places to be confident in the global record.
Interestingly, it's also shortly after the time
we call the Industrial Revolution.
when humans started putting significant amounts of carbon dioxide in the atmosphere,
but we’ll get back to that later.
There are millions of measurements over the last hundred and 40 odd years.
We put those together.
We're using data from literally tens of thousands
of different stations around the world.
We use the information that's there to create a global picture
of what's happening.
And that gives us a very accurate
estimate of how any year ranks or what the
what the anomaly is for any one year compared to what happened
in the 19th century or what happened in the middle of the 20th century.
So we have our statistical reconstruction of Earth's recent climate.
But in research science, we like to check our work.
There are a couple of ways we can do this.
First of all, teamwork. Our colleagues at NOAA, and at other agencies
and universities around the world, also create their own records, and
we can line them up side-by-side, and see just how closely they align.
Everyone's independent climate records show the same thing:
Earth is warming significantly and rapidly.
And here at NASA, we have an even cooler way to check our work:
space!
Right now, we have more than
two dozen satellites dedicated just to studying our planet.
Satellites can take measurements of the entire planet,
and line them up with our estimate of global temperature change.
And sure enough,
they also match!
Our measurements from space match up well with what our analysis tell us:
Earth's climate is warming.
The next big question,
why is our planet warming?
Let’s jump back to the Industrial Revolution:
The release of carbon, mostly carbon dioxide
from human activities like driving cars, flying planes, and industrial burning
of fossil fuels is responsible for the majority of climate change.
Carbon exists in stores underground,
as oil, gas and coal.
When we burn it, we release it into our atmosphere, where it traps
excess heat coming from
the Sun, raising the temperature.
We’ve known for more than a century
that carbon dioxide added to our atmosphere traps
additional heat and is a major contributor
to the greenhouse effect.
So we can also track the
concentration of carbon dioxide in our atmosphere,
the primary cause of the current climate change.
Both from space -- using NASA satellites like
the Orbiting Carbon Observatories 2 and 3 -- and from the ground.
If you’ve heard of the Keeling Curve, you’re familiar with one of these records:
Researchers have been taking daily
measurements of atmospheric carbon dioxide from Mauna Loa, Hawaii,
since the 1950s.
From space and the ground,
the signal is clear:
There’s a lot more carbon in the atmosphere than there used to be.
Other things have changed too - we’ve chopped
down tropical forests,
caused the ozone hole, and
filled the air with soot, smog and
other kinds of air pollution.
And this is on top of natural variations
caused by the dynamics of the oceans, or volcanoes,
or variations in the Sun’s activity.
And so we can ask whether
it’s human activities warming our planet.
At NASA, we have some big and
powerful computers,
able to make 6.8 trillion calculations per second.
We put these huge supercomputers
to work to recreate Earth’s climate.
So, we have thousands of ideas of
what could naturally cause climate change.
We have 4 billion years of history where nearly
anything and everything
you could imagine has impacted Earth's climate!
But each of those events have
their own distinct fingerprint which we can
identify a pattern of behavior with natural variability.
Using supercomputers, we can run simulations of natural climate drivers,
solar energy changes, wobbles in Earth’s orbits, ocean turnover,
volcanic eruptions....
And we can run simulations of human effects.
And what we've seen is...
It's us. There's no way around it.
Looking at the evidence, we're the force that's enacting these changes.
I am so proud of our ability to understand
the climate, but I'm terrified of what we found.
But it’s not just the causes of climate change.
It’s also the effects.
Because it’s not just about knowing why our planet is warming
it’s also about understanding, and preparing for,
the effects of added warmth.
Measurement of global average temperatures is so important
because it's one of the most direct indicators of Earth's changing climate.
But the Earth is really a system of environmental systems, land,
ocean atmosphere and ice, and changes in one system impact the others.
Our oceans are our first line of defense in climate change
because they absorb so much of the extra trapped energy in the Earth system.
We are seeing the impacts of climate change now.
Now we know that as our climate warms,
wet areas are getting wetter and dry areas are getting drier.
For example, we see more intense snowstorms.
We see slower hurricanes that are causing more precipitation that inundate land.
And we have more extreme precipitation in the form of atmospheric rivers
that come from the Pacific and reach our West Coast.
The oceans are observing a large amount of heat because of climate change.
And once that heat is in the ocean, it actually travels all around the planet
because of the ocean currents.
And that has impacts on local weather and long-term climate.
As the planet warms.
It's not just the ocean that's warming, it's also the ice
that sits in the ocean and on land.
The ice on land being warmed increases melting, which is increasing freshwater
input into the polar oceans and causing sea levels to rise across the globe.
So as the climate is changing, we really are
seeing a lot of changes to the environment up in the Arctic.
We're seeing more permafrost
thaw when it's warmer up there,
the warmer air temperature can lead to warm ground temperature
and we get that thawing of that permafrost layer.
We're finding that the fire season
is being exacerbated by longer periods of drought and decreased snowfall.
Knowing that our climate is changing due to human activities means that we know how
to lessen the effects of future warming and knowing how we know
what causes climate change confirms that our efforts would be meaningful.
The situation is serious, but it's not hopeless.
Together, we can decide to make.
A better choice.