Are We Getting Warmer?

Is the Earth getting warmer? 1.Yes 2.No

Is change in the Earth’s climate mostly caused by natural causes or by humans? 1.Natural causes 2.Humans

How do you measure a planets temperature?  If you have them, then thermometers spread around the earth can tell us the average temperature.  These record go back to the mid 19 th century.  Earlier records not standardized so they have more uncertainty.

What affects individual temperature measurements? 1.Geographic variations 2.Local microclimates 3.Land use/heat islands 4.Technique 5.Land or sea 6.All of the above

 Records must account for sea surface temperature, heat islands around cities, land use changes, measurement techniques.  Thermometers may differ in calibration.  Look for trends in temperature rather than absolute temperatures.  Usually want to determine anomalies rather than absolute values.  Anomalies are deviations from average temperature.

Regional Patterns  Warming is greater on land than in oceans (specific heat)  Warming is larger in northern hemisphere (more land and more GHG)  Arctic has warmed at twice the global rate –Ice-albedo feedback, –lower evaporation; more energy directly to the surface

Regional Temperature Anomlies

Zonal Mean Temperature Anomolies

Is the temperature rise unusual?  Before 1850 we have very little direct thermometric data so we use “proxies” for measuring the temperature from long ago.  Examples: tree rings, lake sediments, bleaching of coral reefs, isotope ratios

Temperature for 1000 years.

Greenland Ice Cores

CO 2 and Temperature are strongly correlated.  Probably not cause and effect.

Correlation  Chronological relationship between two factors  Expressed as a number between -1 and 1  Does not prove causal relationship –Rising of Sirius  flooding of the Nile –Coming to physics class  falling asleep

CO 2 and Temperature are strongly correlated.  Probably not cause and effect.  Small chances in temperature are caused by small orbital changes.  Small increase in sea surface temperature causes some CO 2 to come out of solution.  Increase in land surface temperature increases microbial action  more CO 2  More CO 2 in the air cause further warming.

 Using Isotope ratios we can go back millions to billions of years to find temperatures. – 16 O vs. 18 O – 1 H vs. 2 H  Compare ratios in different layers of ice.  Arctic yields clearer results.

Evidence for Rapid Temperature Changes in Greenland Ice Core

Younger Dryas  The Big Freeze  Approximately 15,000 years ago; 1300 year duration  Caused by collapse of North American ice sheets(?)  Believed to be nonlinear effects due to changes in ocean circulation when there was a large influx of fresh water from glacial melting

Ocean Currents

 Caution: The rapid fluctuation in the Younger Dryas are Arctic temperatures which exaggerate global climate changes.  Fluctuation not so obvious in proxies from other regions of the world.  The rapid changes that we are experiencing now are global. They are also more exaggerated in the polar regions.

Reduction in Sea Ice

Decline in Sea Ice

 Not only is there less area of sea ice, it is also thinner.

Melting Glaciers

Global Warming Indicators  Global temperature  Ice sheets (Greenland, Antarctic)  Arctic sea ice  Glaciers  Ocean surface temperature  Sea level

Is the Warming Anthropogenic?

Chicago Tribune 31 March 2006