Climate Change on Geological Timescale

Paleoclimate records provide rich information about temporal evolution of climate on different timescales. Reconstructions of past climate changes are now extensively used as a test bed for the climate models to assess their performance for the climate conditions different from the present one. Past climate changes have also been used to assess climate sensitivity to change in the atmospheric CO2 concentration. At last, past climate changes clearly demonstrate a strongly nonlinear response of the climate system to gradual changes in external forcing and hence indicate a possibility of the existence of some thresholds, crossing of which could lead to irreversible climate change.

On the geologic timescales (tens and hundreds of million years), paleoclimate records provide a strong support to the dominant control of the atmospheric CO 2 concentrations on the Earth's climate, although other factors, such as changes in Earth's geography, also played an important role. Over the past tens of million years climate progressively cooled, and some 3 million years ago a periodic widespread glaciation of the Northern Hemisphere began. The cycles of waning and waxing of the Northern Hemisphere ice sheets became progressively stronger and longer with time (Figure 1a). The last million years were dominated by 100 000-years cycli-city, the nature of which is still not fully understood. However, a strong coupling between ice volume and CO2 concentrations (Figure 1b) suggests that the latter represent an important feedback in the climate system amplifying and shaping the glacial cycles. During the peak of the last glacial cycle, about 21 000 years BP, the globally averaged temperature was about 5 °C below present, with a large portion of this cooling explained by a lowering of the concentration of the major greenhouse gases. In particular, atmospheric CO2 concentration at that time was only two-thirds of its preindustrial value and almost one-half of the current CO2 concentration.

3000 2500 2000 1500

1000

3000 2500 2000 1500

1000

(p240 g 220 200 180

(p240 g 220 200 180

Figure 1 Past climate changes on different timescales. (a) Temporal variations of 18O isotope concentration in marine sediments over the past 3 million years. This isotope represents a proxy for the global ice volume. (b) Variations of CO2 concentration in ppm (black line) versus variations of global ice volume (blue line) over the past 400 000 years. (c) Greenland temperatures from the GRIP ice core during the last 80 000 years. Ice volume data are from Lisiecki LE and Raymo ME (2005) A Pliocene-Pleistocene stack of 57 globally distributed benthic <518O records. Paleoceanography 20: doi:10.1029/2004PA001071; concentration of CO2 is from Petit JR, Jouzel J, Raynaud D, etal. (1999) Climate and atmospheric history of the past 420000 years from the Vostok ice core, Antarctica. Nature 399: 429-436; and Greenland temperature record is based on Daansgard W, Claussen HB, Gundestrup N, et al. (1982) A new Greenland deep ice core. Science 218: 1273-1277.

Figure 1 Past climate changes on different timescales. (a) Temporal variations of 18O isotope concentration in marine sediments over the past 3 million years. This isotope represents a proxy for the global ice volume. (b) Variations of CO2 concentration in ppm (black line) versus variations of global ice volume (blue line) over the past 400 000 years. (c) Greenland temperatures from the GRIP ice core during the last 80 000 years. Ice volume data are from Lisiecki LE and Raymo ME (2005) A Pliocene-Pleistocene stack of 57 globally distributed benthic <518O records. Paleoceanography 20: doi:10.1029/2004PA001071; concentration of CO2 is from Petit JR, Jouzel J, Raynaud D, etal. (1999) Climate and atmospheric history of the past 420000 years from the Vostok ice core, Antarctica. Nature 399: 429-436; and Greenland temperature record is based on Daansgard W, Claussen HB, Gundestrup N, et al. (1982) A new Greenland deep ice core. Science 218: 1273-1277.

Was this article helpful?

0 0
Worm Farming

Worm Farming

Do You Want To Learn More About Green Living That Can Save You Money? Discover How To Create A Worm Farm From Scratch! Recycling has caught on with a more people as the years go by. Well, now theres another way to recycle that may seem unconventional at first, but it can save you money down the road.

Get My Free Ebook


Post a comment