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In 1988, Dr. James Hansen,

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then Director of NASA's Goddard Institute
for Space Studies, stood before the U.S.

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Senate and testified that...

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Global warming has reached a level such
that we can ascribe

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with a high degree of confidence,
a cause and effect relationship

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between the greenhouse effect
and observed warming....

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It is already happening now.

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This last year, 2021,

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comes in as the sixth warmest year on record,

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and it continues this large

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long-term warming that Jim Henson

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was detecting even in 1988.

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and in 1988, that was also a globally warmest year.

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But now that ranks only 28th in the
in the ranking.

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And so the warming that we've had since

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Jim Hansen's testimony has been dramatic
and totally vindicates

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that concern and the warnings
that he put out at that time.

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The Goddard Institute for Space Studies,
or GISS

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for short, maintains NASA's
record of Earth's surface temperature,

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called GISTEMP,  that shows a clear and unequivocal

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increase in our planet's temperature.

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GISTEMP stretches from 1880,

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long before NASA's existed,
until the present day.

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Now, when you think of NASA, you

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probably think of, well, space, right?

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And we do lots of work studying Earth from above.

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but the GISTEMP record is actually built from the ground up

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We collect measurements

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taken from weather stations,
Antarctic research stations.

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And ships and ocean buoys
all around the planet to understand

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what temperature changes
look like globally.

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And why does the record start in 1880?

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That's the earliest period that we have sufficiently reliable

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measurements from ships
and weather stations

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in enough places
to be confident in the global record.

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Interestingly, it's also shortly
after the time

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we call the Industrial Revolution.

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when humans started putting significant amounts of carbon dioxide in the atmosphere,

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but we’ll get back to that later. 

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There are millions of measurements
over the last hundred and 40 odd years.

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We put those together.

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We're using data
from literally tens of thousands

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of different stations around the world.

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We use the information
that's there to create a global picture

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of what's happening.

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And that gives us a very accurate

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estimate of how any year ranks or what the

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what the anomaly is for
any one year compared to what happened

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in the 19th century or what happened
in the middle of the 20th century.

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So we have our statistical reconstruction
of Earth's recent climate.

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But in research science,
we like to check our work.

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There are a couple of ways
we can do this.

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First of all, teamwork. Our colleagues at NOAA, and at other agencies

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and universities around the world, also create their own records, and

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we can line them up side-by-side, and see just how closely they align. 

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Everyone's independent climate records
show the same thing:

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Earth is warming significantly and rapidly. 

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And here at NASA, we have an even cooler way to check our work:

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space!

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Right now, we have more than

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two dozen satellites dedicated
just to studying our planet.

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Satellites can take measurements of the entire planet,

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and line them up with our estimate of global temperature change. 

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And sure enough,

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they also match!

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Our measurements from space match up well with what our analysis tell us:

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Earth's climate is warming.

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The next big question,

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why is our planet warming?

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Let’s jump back to the Industrial Revolution:

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The release of carbon, mostly carbon dioxide

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from human activities like driving cars, flying planes, and industrial burning

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of fossil fuels is responsible for the majority of climate change. 

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Carbon exists in stores underground,

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as oil, gas and coal.

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When we burn it, we release
it into our atmosphere, where it traps

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excess heat coming from

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the Sun, raising the temperature.

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We’ve known for more than a century

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that carbon dioxide added to our atmosphere traps 

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additional heat and is a major contributor

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 to the greenhouse effect.

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So we can also track the

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concentration of carbon dioxide in our atmosphere,

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the primary cause of the current
climate change. 

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Both from space -- using NASA satellites like

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 the Orbiting Carbon Observatories 2 and 3 -- and from the ground.

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 If you’ve heard of the Keeling Curve, you’re familiar with one of these records: 

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Researchers have been taking daily

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measurements of atmospheric carbon dioxide from Mauna Loa, Hawaii,

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since the 1950s. 

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From space and the ground,

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the signal is clear: 

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There’s a lot more carbon in the atmosphere than there used to be. 

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Other things have changed too - we’ve chopped 

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down tropical forests, 

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caused the ozone hole, and

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 filled the air with soot, smog and

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other kinds of air pollution.

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And this is on top of natural variations

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caused by the dynamics of the oceans, or volcanoes,

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or variations in the Sun’s activity. 

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And so we can ask whether

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it’s human activities warming our planet.

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At NASA, we have some big and

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powerful computers,

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 able to make 6.8 trillion calculations per second.

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We put these huge supercomputers

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to work to recreate Earth’s climate.

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So, we have thousands of ideas of

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what could naturally cause climate change.

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We have 4 billion years of history
where nearly

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anything and everything

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you could imagine has impacted Earth's climate!

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But each of those events have

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their own distinct fingerprint which we can 

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identify a pattern of behavior with natural variability. 

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Using supercomputers, we can run
simulations of natural climate drivers,

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solar energy changes, wobbles in Earth’s orbits, ocean turnover,

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volcanic eruptions....

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And we can run simulations of human effects. 

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And what we've seen is...

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It's us.  There's no way around it.

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Looking at the evidence, we're the force
that's enacting these changes.

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I am so proud of our ability to understand

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the climate, but I'm terrified of what we found.

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But it’s not just the causes of climate change.

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It’s also the effects.

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Because it’s not just about knowing why our planet is warming

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it’s also about understanding, and preparing for,

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the effects of added warmth.

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Measurement of global average temperatures is so important

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because it's one of the most direct
indicators of Earth's changing climate.

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But the Earth is really a system
of environmental systems, land,

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ocean atmosphere and ice, and changes
in one system impact the others.

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Our oceans are our first line of defense
in climate change

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because they absorb so much of the extra
trapped energy in the Earth system.

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We are seeing the impacts
of climate change now.

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Now we know that as our climate warms,

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wet areas are getting wetter
and dry areas are getting drier.

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For example, we see more intense snowstorms.

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We see slower hurricanes that are causing
more precipitation that inundate land.

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And we have more extreme precipitation
in the form of atmospheric rivers

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that come from the Pacific
and reach our West Coast.

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The oceans are observing a large amount
of heat because of climate change.

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And once that heat is in the ocean,
it actually travels all around the planet

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because of the ocean currents.

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And that has impacts on local weather and long-term climate.

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As the planet warms.

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It's not just the ocean
that's warming, it's also the ice

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that sits in the ocean and on land.

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The ice on land being warmed increases
melting, which is increasing freshwater

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input into the polar oceans and causing
sea levels to rise across the globe.

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So as the climate is changing,
we really are 

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seeing a lot of changes
to the environment up in the Arctic.

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We're seeing more permafrost

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thaw when it's warmer up there,

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the warmer air temperature can lead
to warm ground temperature

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and we get that thawing
of that permafrost layer.

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We're finding that the fire season

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is being exacerbated by longer periods
of drought and decreased snowfall.

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Knowing that our climate is changing due
to human activities means that we know how

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to lessen the effects of future warming
and knowing how we know

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what causes climate change confirms
that our efforts would be meaningful.

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The situation is serious,
but it's not hopeless.

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Together, we can decide to make.

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A better choice.