Lecture 35: The Global Warming DebateLecture 35: The Global Warming Debate

Ch. 18

The Global Warming Debate

Ch. 17, Ch. 18

1. Is global warming real? (Or is global warming happening?)

2. What is the evidence?

3. Is global warming part of natural cycles? Or is it caused by humans? Why?

4. Why do we care about global warming?

5. How much warming is caused by humans?

Data over the globe (land and sea). Data over the globe (land and sea). Warming periods: 1900-1945 (by 0.5Warming periods: 1900-1945 (by 0.5°°C), the mid-1970s to present.C), the mid-1970s to present.The warmest decade: the 1990s. The warmest year: 2005, 1998. The warmest decade: the 1990s. The warmest year: 2005, 1998. 2001 sixth warmest year on record. Over last 25 years warming ~ 0.5 COver past century warming ~ 0.75 CCooling periods: 1945-1975.Cooling periods: 1945-1975.

Temperature Trends in the 20Temperature Trends in the 20thth Century Century

http://www.ucsusa.org/global_warming/science/recordtemp2005.html

Surface Air Temperature Trends Over the Past CenturySurface Air Temperature Trends Over the Past Century

Warming greatest Warming greatest at nightat night over northern over northern mid-to-high latitude land mid-to-high latitude land Stronger warming Stronger warming during during winter and springwinter and spring Greater than the global average in some areasGreater than the global average in some areasCooledCooled in some areas (southern Mississippi Valley in USA) in some areas (southern Mississippi Valley in USA)

www.gcrio.org/ipcc/qa/02.html

USA 100-yr Temperature TrendsUSA 100-yr Temperature Trends

Temperatures have actually Temperatures have actually cooledcooled, e.g., over the , e.g., over the southernsouthern Mississippi ValleyMississippi Valley in North America. in North America.

The Earth’s Climate History1. Over the last century, the earth’s surface temperature has increased by

about 0.75°C (about 1.35°F).

2. Little Ice Age = Cooling during 1,400 A.D. – 1,900 A.D. (N.H. temperature was lower by 0.5°C, alpine glaciers increased; few sunspots, low solar output)

3. Medieval Climate Optimum (Warm Period) = Warming during 1,000 A.D. – 1,300 A.D. in Europe and the high-latitudes of North Atlantic (N.H. warm and dry, Nordic people or Vikings colonized Iceland & Greenland)

4. Holocene Maximum = 5,000-6,000 ybp (1°C warmer than now, warmest of the current interglacial period)

5. Younger-Dryas Event = 12,000 ybp (sudden drop in temperature and portions of N.H. reverted back to glacial conditions)

6. Last Glacial Maximum = 21,000 ybp (maximum North American continental glaciers, lower sea level exposed Bering land bridge allowing human migration from Asia to North America)

7. We are presently living in a long-term Icehouse climate period, which is comprised of shorter-term glacial (e.g., 21,000 ybp) and interglacial (e.g., today) periods. There were four periods of Icehouse prior to the current one.

8. For most of the earth’s history, the climate was much warmer than today.

Uncertainties about the Global Warming of the Past Century

Skeptics

a. No warming discernable in data

b. If warming, not from human activities The sunspot cycle The role of ozone

The role of clouds The role of sulphate aerosols

The role of dust The role of oceans

c. If warming, and from human activities, maybe warming not so bad

d. If warming, and from human activities, and it is a problem, then engineer a solution to pull CO2 out of the atmosphere, e.g., through carbon sequestration, while conducting other business as usual (i.e., don’t cut CO2 emissions).

Uncertainties in the temperature dataearly records are subject to instrumental error and improper sitting

uneven land and sea stations

too many Northern Hemisphere records

urban heat island effect

mismatch between satellite, balloon and surface data

ALL THESE HAVE BEEN CAREFULLY ACCOUNTED FOR OR MOSTLY RESOLVED

Natural Warming and Greenhouse EffectsNatural Warming and Greenhouse Effects

Observed Temperature Changes and Natural Observed Temperature Changes and Natural ContributionsContributions

Observed trend 0.6Observed trend 0.6°°C/centuryC/century

Components of 2 Components of 2 ×× CO CO22 Warming Warming

Model Simulations of 2 x COModel Simulations of 2 x CO2 Sensitivity Sensitivity

Earth’s CO2 Sensitivity from Climate ModelsEarth’s CO2 Sensitivity from Climate Models

Earth’s CO2 Sensitivity from Earth HistoryEarth’s CO2 Sensitivity from Earth History

Uncertainties about the Global Warming of the Past Century

Skeptics

a. No warming discernable in data

b. If warming, not from human activities The sunspot cycle The role of ozone

The role of clouds The role of sulphate aerosols

The role of dust The role of oceans

c. If warming, and from human activities, maybe warming not so bad

d. If warming, and from human activities, and it is a problem, then engineer a solution to pull CO2 out of the atmosphere, e.g., through carbon sequestration, while conducting other business as usual (i.e., don’t cut CO2 emissions).

Uncertainties in the temperature dataearly records are subject to instrumental error and improper sitting

uneven land and sea stations

too many Northern Hemisphere records

urban heat island effect

mismatch between satellite, balloon and surface data

ALL THESE HAVE BEEN CAREFULLY ACCOUNTED FOR OR MOSTLY RESOLVED

Radiative Effects of Greenhouse GasesRadiative Effects of Greenhouse Gases

Effects of Increases in Greenhouse Gases on RadiationEffects of Increases in Greenhouse Gases on Radiation

Marine Aerosols from Algal Emissions can affect Climate

O’Dowd et al., Marine aerosol formation from biogenic iodine emissions, Nature 417, 632 - 636 (2002)

Thank You!