Global Climate Change

The Evidence and

Human Influence

Principle Evidence

CO2 and Temperature

Temperature Patterns

Climate Change

Climate is the average weather at a given point and time of year, over a long period (typically 30 years).

We expect the weather to change a lot from day to day, but we expect the climate to remain relatively constant.

If the climate doesn’t remain constant, we call it climate change.

The key question is what is a significant change? This depends upon the underlying level of climate

variability It is crucial to understand difference between climate

change and climate variability…

Temperature Patterns

Variations of the Earth’s surface temperature for the past 140 years

Temperature Patterns

100 0.0740.018

50 0.1280.026

Warmest 12 years:1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999,1990,2000

Period Rate

Years /decade

Is It Real?

Earth is getting warmer by virtually every measure we know, and the temperature has been well above normal for more than 25 years.

Is It Real?

Although increases of 1.0-1.6oF (0.6-0.9oC) over the last century or so may not sound very threatening, remember that’s a global average.

Area of seasonally frozen ground in NH has decreased by 7% from 1901 to 2002

Spring snow covershows 5% stepwise drop during 1980s

Arctic sea ice area decreased by 2.7% per decade(Summer: -7.4%/decade)

Rise in global ocean heat content 1955-2005 Earth is getting warmer by

virtually every measure we know, and the temperature has been well above normal for more than 25 years.

Although increases of 1.0-1.6oF (0.6-0.9oC) over the last century or so may not sound very threatening, remember that’s a global average.

The warming is stronger over land than over oceans and in the higher latitudes than in the tropics.

Sea-level from satellites: 4 cm rise in last 10 years

Could the warming be natural?

Certainly, past temperatures have been higher (and lower) than today, and

CO2 concentrations have also varied.

Large global swings were probably caused by such things as changes in Earth’s orbit, which changed the distribution of sunlight over the planet.

When this caused warming, more CO2 and other greenhouse gases were released, producing additional warming.

Could the warming be natural?But today, the CO2 released by human activities is far above amounts in the previous 800,000 years. This CO2 is triggering the increase in temperatures we’ve seen.

Mauna Loa CO2 observations

The data on atmospheric CO2 collected by Keeling at the Mauna Loa observatory is said to be the most widely seen data set in the world.

It was started in 1955 CO2 was at 313 ppm It was at 389 ppm in 2010 an increase of

19.5% in 55 years In February of 2015 it exceeded 400ppm

CO2 Levels

CO2 Levels

Summary (Observations)

Global surface temperatures have risen by about 0.6°C since 1900

It is likely that this warming is larger than for any century since 200AD, and that the 1990s were the warmest decade in the last millennium.

The warming differs in different parts of the world, but over the last 25 years, almost everywhere has warmed, and very few places have cooled.

Other changes have occurred Sea level has risen by about 20 cm, Ocean heat content has increased, Almost all mountain glaciers have retreated

Summary (Observations)

Coincident with this global warming, levels of CO2 (and other ‘greenhouse’ gases) have dramatically increased, to levels higher than those experienced for maybe millions of years.

Question: are temperatures and atmospheric composition linked?

Global Warming Potentials

• Refers to the relative ability of one molecule of a given greenhouse gas to contribute to warming.

• Values are expressed in relation to CO2, which is assigned a global warming potential of 1.