geography final worksheet

Long-term carbon cycle and global temperature trend

Keeling curve

This is one of the most important figures on climate change showing the monthly CO2 observation record measured at Mauna Loa Observatory in Hawaii since 1958. This graph showing a continuous measurement of CO2 is called the “Keeling Curve”, named after Dr. Charles David Keeling, who initiated and directed this measurement in the 1950s. This graph has great importance such that it is carved into one of the walls at the National Academy of Sciences in Washington D.C.

Why it is so important?

Because this graph, measurements taken directly from the atmosphere, is amongst the strongest evidence to prove that the atmospheric concentration of CO2 is actually increasing!

Further reading: Keeling Curve Lessons http://scrippsco2.ucsd.edu/history_legacy/keeling_curve_lessons Keeling Curve – A Daily Record https://scripps.ucsd.edu/programs/keelingcurve/

https://www.esrl.noaa.gov/gmd/ccgg/trends/

This graph shows the most recent CO2 measurements taken at the Mauna Loa

Observatory. The dashed red line represents the monthly mean values. The black line with the square symbols represents the monthly mean values with correction applied

for the average seasonal cycle (for further reading:

https://www.esrl.noaa.gov/gmd/ccgg/trends/). When you zoom into the last 6 years

of Keeling Curve, you will find a long-term trend that consistently increases

throughout the period (e.g. CO2 value in the beginning of the year is consistently

higher year after year). Also, you see ups and downs within each year.

What do the ups and downs mean? Please know that climate skeptics/deniers use

this graph and say that the CO2 value is decreasing…! Is that true?

For the answer, please see the follwing slide.

Atmospheric CO2 concentrations

Atm. CO2 levels rise again as plants & leaves die/decay & release CO2 back into the atmosphere.

New plant growth removes atm CO2 through photosynthesis

Year

� Keeling Curve: plots the concentration of carbon dioxide in Earth's atmosphere since 1958.

� Charles David Keeling

� Based on continuous measurements taken in Hawaii.

� 1958 = 315 ppm � Sept. 2016 = 402 ppm

In 2022….?

CO2 increases and decreases within a year is a seasonal variation showing carbon fixation by the plants. Can we use this fact as evidence of decreasing CO2 in the atmosphere? No! It is very important that we look into long-term variability and not seasonal variability when we discuss climate change.

If we continue to release carbon dioxide at the current speed, then what happens? One example can be seen using an ordinary coastal town like this, which shows what will eventually happen…

(continue)

12 feet: 4 meters

this, and…

(continue)

25 feet= 8 meters

eventually uninhabitable.

Last Ice Age

Present

As we have already seen, Earth’s climate has been naturally changing throughout its history. In this figure, what you see are the long-term ups and downs of CO2 concentration in the atmosphere. This trend shows glacial/interglacial cycles for the past 450,000 years. High CO2 intervals coincide with interglacial (warm) periods and low CO2 intervals coincide with glacial (cold) periods. Based on this figure, the most recent glacial period ended about 12,000 years ago and we are experiencing a somewhat warm climate. That said, please note that the current atmospheric CO2 concentration is far beyond any of the values the Earth experienced in the past 450,000 years.

Now, we know that the Keeling Curve is a direct measurement of the atmosphere after 1958. Then, how do we know what pre-historic (throughout the prior hundreds of thousand of years) atmospheric CO2 values are?

(Please see next slide!)

Atmospheric CO2 concentrations � How can past atmospheric CO2 concentrations be determined? � Ice cores contain trapped bubbles of gas. � This gas reflects the atmospheric composition at the time the ice was formed.

Also, from the gas bubbles in the ice core, we can measure pre-historic values of other greenhouse gases. Not only CO2, CH4 also show a similar ups and downs.

Greenhouse Gas Concentrations � Human activities result in emissions of 4 principal greenhouse gases:

1. carbon dioxide (CO2) 2. methane (CH4) 3. nitrous oxide (N2O) 4. halocarbons (a group of gases containing fluorine, chlorine and bromine)

� These gases accumulate in the atmosphere, causing concentrations to increase with time.

� Significant increases in all of these gases have occurred in the industrial era. All of these increases are attributable to human activities.

4.2.4 Tropospheric O3 Tropospheric O3 is a direct greenhouse gas. The past

increase in tropospheric O3 is estimated to provide the

third largest increase in direct radiative forcing since the

pre-industrial era. In addition, through its chemical

impact on OH, it modifies the lifetimes of other

greenhouse gases, such as CH4. Its budget, however, is

much more difficult to derive than that of a long-lived gas

for several reasons. Ozone abundances in the

troposphere typically vary from less than 10 ppb over

remote tropical oceans up to about 100 ppb in the upper

troposphere, and often exceed 100 ppb downwind of

polluted metropolitan regions. This variability, reflecting

its rapid chemical turnover, makes it impossible to

determine the tropospheric burden from the available

surface sites… (IPCC TAR 2001)

Here is a quote from the IPCC’s assessment report published in 2001. In addition to the previously mentioned greenhouse gases, tropospheric ozone is also a potent greenhouse gas. And as you will see in the following slide, there is a skewed geographical distribution of ozone emissions as a result of industrialization, agriculture, and urbanization.

Please note that the tropospheric ozone we mention here is found near the surface of the Earth and is different from stratospheric ozone (upper atmospheric ozone, where we observe the ozone hole over Antarctica).