Climate Change: Is it real? Countering the Skeptics’ Statements:

You be the climate scientist.

“CO2 is not increasing”“Humans contribute only a small percent to CO2

emissions”"It's cooling"

“It’s a natural cycle”“Extreme weather isn’t caused by global

warming”“Sea level isn’t rising”

“Ice isn’t melting”

“CO2 is not increasing”

Changes in Global CO2 Concentrations

Skeptic Statement: CO2 is not increasing

Source: NASA

Different scenarios for the future

Skeptic Statement: CO2 is not increasing

Direct atmospheric measurements of CO2 since 1958

Annual cycle of ~ 5 ppm due to seasonal uptake of CO2 by (overwhelmingly northern hemisphere) vegetation

1958 = 315 ppm 2008 =

385 ppm

Year

CO2 (

ppm

)

Skeptic Statement: CO2 is not increasing

Annual Global Mean Surface Temperature and Carbon Dioxide Concentrations

0.76ºC (1.4ºF) since 1900 0.55ºC (1.0ºF) since 1979

Source: Jim Hurell, NCARSkeptic Statement: CO2 is not increasing

“Humans contribute only a small percent to CO2 emissions”

Figure 1: Atmospheric CO2 levels (Green is Law Dome ice core, Blue is Mauna Loa, Hawaii) and Cumulative CO2 emissions (CDIAC). While atmospheric CO2 levels are usually expressed in parts per million, here they are displayed as the amount of CO2 residing in

the atmosphere in gigatonnes. CO2 emissions includes fossil fuel emissions, cement production and emissions from gas flaring.

“Humans contribute only a small percent to CO2 emissions”

Figure 1: Observed increase atmospheric CO2 derived from direct measurements, taking the average of Mauna Loa (Hawaii) and the South Pole (thin solid line) and two ice cores: Law Dome (dashed thin line) and Siple (thin dotted line). This is compared to total anthropogenic emissions (thick solid line) and 46% of total emissions (thick dashed line). (Knorr 2009)“Humans contribute only a small percent to CO2 emissions”

Figure 1: Global carbon cycle. Numbers represent flux of carbon dioxide in gigatons (Source: Figure 7.3, IPCC AR4).

“Humans contribute only a small percent to CO2 emissions”

“Extreme weather isn’t caused by global warming”

Anomaly: deviation or departure from normal

“Extreme weather isn’t caused by global warming” Source: Global Change Climate Impacts Report 2009

“Extreme weather isn’t caused by global warming” Source: Global Change Climate Impacts Report 2009

“Extreme weather isn’t caused by global warming” Source: Global Change Climate Impacts Report 2009

Is it global warming, or is it natural variability?These are not the right questions: it is a combination of

both

Heat waves are increasing: an example

“Extreme weather isn’t caused by global warming”

Number of Days Over 100°F

The number of days in which the temperature exceeds100°F by late this century, compared to the 1960s and1970s, is projected to increase strongly across theUnited States. For example, parts of Texas that recentlyexperienced about 10 to 20 days per year over 100°F areexpected to experience more than 100 days per year inwhich the temperature exceeds 100°F by the end of thecentury under the higher emissions scenario.91

“Extreme weather isn’t caused by global warming”

Temperature departure from normal

“It’s a natural cycle”

Courtesy John P. ReismanIt’s a natural cycle

"It's cooling"

Image from NASA 2002 surface temperature summation It’s cooling

Future projections Observed and Projected Temperature Rise for the Southwest

The average temperature in the Southwest has already increased roughly 1.5°F compared to a 1960-1979 baseline period. By the end of the century, average annual temperature is projected to rise approximately 4°F to 10°F above the historical baseline, averaged over the Southwest region. The brackets on the thermometers represent the likely range of model projections, though lower or higher outcomes are possible.

From www.globalchange.gov/usimpacts (Southwest factsheet)It’s cooling

Number of Days Over 100°F

The number of days in which the temperature exceeds100°F by late this century, compared to the 1960s and1970s, is projected to increase strongly across theUnited States. For example, parts of Texas that recentlyexperienced about 10 to 20 days per year over 100°F areexpected to experience more than 100 days per year inwhich the temperature exceeds 100°F by the end of thecentury under the higher emissions scenario.91

Annual Global Mean Surface Temperature and Carbon Dioxide Concentrations

0.76ºC (1.4ºF) since 1900 0.55ºC (1.0ºF) since 1979

It’s cooling

It’s cooling

Is it global warming, or is it natural variability?These are not the right questions: it is a combination of

both

Heat waves are increasing: an example

It’s cooling

“Sea level is not rising”

Measured sea level rise

1.8 mm/yr (20th century)

3.0 mm/yr (satellites)

IPCC 4th assessment report (2007)Sea level is not rising

Graph from Church 2008

Sea level is not rising

Ice isn’t melting

Image source: NASA.) Ice isn’t melting

Side by side comparisons of seaice from 1979 and 2003. source: NASAIce isn’t melting

1979 2003

Arctic Sea Ice

Ice isn’t melting(Image source: National Snow and Ice Data Center.)

Graph: Atmospheric carbon dioxide concentration (ppmv) and temperature change (°C) observed during the past 160 thousand years and predicted during the next 10 thousand years. Historical carbon dioxide data was collected from Antarctic ice cores; temperature changes through time are relative to the present temperature. Graph adapted from the Whitehouse Initiative on Global Climate Change.