User:Gergyl/PT

This shows estimates of global average surface air temperature over the ~540My of the Phanerozoic, since the first major proliferation of complex life forms on our planet. A substantial achievement of the last 30 years of climate science has been the production of a large set of actual measurements of temperature history (from physical proxies), replacing much of the earlier geological induction (i.e. informed guesses). The graph shows selected proxy temperature estimates, which are detailed below.

Because many proxy temperature reconstructions indicate local, not global, temperature -- or ocean, not air, temperature -- substantial approximation may be involved in deriving global surface air temperature estimates. As a result, the relativities of some of the plotted estimates are approximate.

Time scale
Time is plotted backwards from the present, taken as 2015CE. It is scaled linear in five separate segments, expanding by about one order of magnitude at each vertical break. The breaks are not evenly distributed; rather they are positioned at geologically relevant times:


 * At the Mesozoic - Cenozoic boundary, ~65My ago. This is the "K-T" boundary (now called "Cretaceous–Paleogene"), at which the dinosaurs became extinct.
 * At the Miocene - Pliocene boundary, ~5.3My ago.
 * One million years ago, near the onset of the current, 100,000 year-dominated, glaciation cycle (previous glaciations were shorter).
 * Near the last glacial maximum, 20,000 years ago.

Temperature scale
Temperature is plotted as anomalies (differences) from the average over the reference interval 1960-1990, in both Celsius (left) and Fahrenheit (right).

Panel 1, 540 - 65 million years
Data is from stable oxygen isotope measurements from the shells of macro marine organism, collected by Veizer et al, as re-interpreted by Royer et al (2004). The graph effectively reproduces the upper panel of Royer et al's figure 4. The orange band indicates the effects of using the range of then-available CO2 proxies in interpretation, and is not representative of the full uncertainly.

Because the Royer / Veizer temperatures are indicative of the temperature of shallow tropical seas, they are unlikely to be fully representative of global average surface air temperature variation. The temperatures are plotted here expanded by a factor of two, as a very approximate conversion.

Panel 2, 65 - 5.3 million years
This data is from the Hansen et al (2013) interpretation of the global collection of oxygen isotope data from microscopic marine organisms of Zachos et al (2008).

This is a direct estimate of global average surface air temperature.

Panel 3, 5.3 - 1 million years
This data is from the Lisiecki and Raymo (2005) global stack of oxygen isotope data from microscopic marine organisms interpreted using the Hansen et al (2013) prescription.

At this scale, the Zachos stack is virtually indistinguishable from the Lisiecki and Raymo stack over this interval. The latter is retained principally for historical reasons. This is a direct estimate of global average surface air temperature.

Panel 4, 1 million - 20,000 years
Two datasets are plotted:

1. Lisiecki and Raymo as in panel 3.

2. Temperature estimates from hydrogen isotope measurements from the EPICA Dome C ice core from central Antarctica. These temperature estimates are polar, not global, and are here divided by a standard polar amplification factor (2.0, as for example in Hansen et al (2013) ) to approximately convert them to global estimates.

Panel 5, 20,000 years - present (2015)
Five datasets are plotted:

1. EPICA Dome C, as in panel 4.

2. Temperature estimates from oxygen isotope measurements on the north Greenland ice core, NGRIP, interpreted by the simple procedure of Johnsen et al (1989). (There are more modern and complex procedures which would yield slightly different interpretations.) The difference between this and dataset 1. indicates the polar sea saw hypothesis.

3. Global temperature estimates over the ~12,000 years of the Holcene are from the multi-proxy collection and interpretation of Marcott et al (2013)

4. Instrumental (not proxy) data shown since 1850 is from the Berkeley Earth project land-ocean dataset

5. Projected temperatures for 2050 and 2100 are from the IPCC fifth assessment report's working group I summary for policy makers

SVG
See the talk page for an explanation of the adpoted graphical format choice.

Category:Geologic time scale