Land Surface Temperature Records

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From the course by The University of Chicago

Global Warming I: The Science and Modeling of Climate Change

157 ratings

The University of Chicago

Global Warming I: The Science and Modeling of Climate Change

157 ratings

This class describes the science of global warming and the forecast for humans’ impact on Earth’s climate. Intended for an audience without much scientific background but a healthy sense of curiosity, the class brings together insights and perspectives from physics, chemistry, biology, earth and atmospheric sciences, and even some economics—all based on a foundation of simple mathematics (algebra).

From the lesson

Looking for a Human Impact on Climate

You have now seen the ideas behind the forecast for a human impact on Earth's climate. The next question is: Do we see it happening today? It turns out that the "smoking gun" for a human impact on climate is the global average temperature record since about the 1970's. In order to interpret that temperature change, we need to consider it within the context of natural climate changes in Earth's geologic past.

Land Surface Temperature Records4:15

Sea Surface Temperature Records3:20

Satellite Temperature Records2:26

The Smoking Gun: Warming Since the 1970s6:54

Meet the Instructors

David Archer
Professor
Geophysical Sciences

[MUSIC]

So, theory is all well and good, but if we're going to invest money in trying to

limit CO2 emissions to avoid climate change Really we want something more.

We want to have evidence that everything is working

the way it is thought that it should, theoretically.

So the way to do that is to see if the Earth is in fact,

warming up There are three different.

major types of temperature measurements.

Those over land, those over sea and those from satellites.

Land temperature records go back

to the invention of the thermometer by Gabriel Farenheit in 1714.

The thermometer is very easy to calibrate, because you can just stick it in boiling

water, and then stick it in ice water, and make a scale between those two things.

And since we know today what temperatures ice melts and

boils at, It's very easy to interpret

very old thermometer measurements in terms of what the temperature really was.

This is as opposed to say, measurements of CO2 concentration or something like that.

that would've used methods that are hard to reconstruct today.

And so, some kinds of old data are really not worth that much but

old temperature data is pretty reliable.

[SOUND] So one possible problem with the land temperature

measurements is called the urban heat island effect.

This is a very real effect.

The idea is that In a vegetated landscape, the incoming sunlight energy

can be carried back away by the latent heat in water vapor.

Because plants mine water from the ground, and they encourage it to evaporate.

Whereas, in a sort of urban landscape, the same heat input can only be balanced

by warming up the ground enough so that infrared energy

leaving can balance the incoming light.

And so, in maps of temperatures,

or infrared images from space of around cities.

it's very clear that it's warmer in urban environments than it is

in rural environments.

So, the problem would come in if a lot of the places

where they measure temperatures have transitioned over time from

relatively green places like this to relatively urban places like that.

And if you then took the warming that would be due to the urban heat island

effect and you called that global warming due to rising CO2 concentrations,

that would be a wrong attribution.

But there have been many studies that have taken the thermometer data and

put them together into global average temperature change.

And they take different methods of

trying to filter out the urban heat island effect.

from their averages.

by take stations out if they seem like they're likely to be a problem.

And as you can see in this plot, basically everybody's getting the same answer for

the average temperature of the earth.

So, it turns out, that the Urban Heat Island Effect, while it is a very real

effect, Is not an important one for setting the global average temperature.

So it's not confounding the global warming signal

that's being measured by thermometers on land.

[MUSIC]

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