Introduction

Both during the Neogene and the Pleistocene cold times with cold and warm conditions occurred. During the Pleistocene the interglacials had by present-day nomenclature been greenhouse-climates with temperatures 2.5-3.6°C above pre-industrial values.

Especially after 2.75 Ma from these pronounced glacial times started.

While the last glacial maximum (LGM) and the last glacial period (LGP, lasting from about ca. 60.000 a to 18.000 a) have been studied extensively, the warm times before and after the LGP and in betweeen glacials are an area of a wealth of upcoming possibilities. This applies particularly as the future is generally expected to be warm and not cold.

If orbital parameters did not change during the earth history such as by meteoritic impacts or fly-bys their impact on the global climate as expressed by the ice-volume varied through time. This applies both to the time before and after 2.75 Ma and before and after 1 Ma. A change of other important boundary conditions, such as in the ocean circulation, important parts of orography (Andes, Tibet Plateau) is to be tested.

Another related question that is of importance for the future is the persistence of the Holocene climatic conditions.

Once the preceding pleistocene greenhouse climate (inter-glacials) had been established glacials conditions had been approached again. If the conditions of the second but last glacial would have ocurred from 11.600 a on, then today values of -4.5 C should be observed. If the conditions of the third but last glacial are applied (Vostok ice-core, Petit et al. 1999) then today values of -8.5 C should be observed.

As compared to earlier times the Holocene is remarkably stable at least one boundary condition for a reglaciation was not met again. If orbital parameters did not change 11.600 years ago those parameters of the geosystem need to be tested that are able to have a respective impact on climate.

Based on this a prediction for the duration of the current warm times is made. The author regards this prediction as one possible co-answer that sheds light on important aspects of the geosystem. There might have been times were other parameters had been more important.

There might also have been times (see the details of the Vostok ice-core) where deglaciations ended abruptly. Thus all important aspects of climate change including the deep ocean circulation, submarine landslides, orograhic changes including isostasy at various parts of the earth need to be considered.

One important factor of climate change is the global radiation balance.

To assess this based on hard data, both during glacials and interglacials, not only the extent of ice covers needs to be known but also their impact on the radiation balance. High latitude ice-sheets, possibly also in low altitudes, have for geometrical reason a much smaller impact on the radiation balance than low latitude ice-sheets in high altitudes.

This means that works that study Neogene and Quaternary climate change need to know the extent of subtropical ice-sheets and, for reasons of isostasy, also their thickness, that for example atmospheric general circulation models need to meet as milestones.

Knowledge on all Neogene and Quaternary ice-sheets that might have existed in low latitudes is difficult if not impossible to obtain. Given the regular pattern of the Vostok ice-core, at least for the last 400 000 years, ice extensions and thicknesses that have similarities to that from the LGM (LGP) can be expected.

Thus, for subtropical latitudes from High Asia (Himalaya and Tibet to Sayan Mts., Siberia) field evidence on extensions, thicknesses and timing of ice-sheets have been determined. The field evidence differs remarkably from the reconstructions of CLIMAP (Cline 1981). As also older field data are in agreement with the data of the author, the field evidence is presented as reference data-base.

After that the radiation-balance is discussed.

Following that the isostatic impact of that ice-sheet is outlined.

Independent of the interpretation of the isostatic impact the hard data of the extension of the ice-sheets that have to be met by atmospheric general circulation models are of value beyond this contribution.

This work discusses the following aspects:

2. Empirical Data

2.1. Overview of existing knowledge

2.2 Evidence of a large Inland-ice on the Tibet Plateau (2.2.1.-14.)

2.3. Ice-thickness, lowest postion of ice-margins around the Tibetan Plateau and the depression of the equilibrium line during the Last Glacial Period (LGP) (2.3.1. - 2.3.18.)

3. Synopsis of the extent of the Inland-Ice in Tibet since the earliest LGP

4. The Tibet Plateau - A stabilizing factor for the climate system

4.1. The Radiation Balance

4.2. Isostatic Impact of the Tibetan Inland Ice

4.3. Impact of orbital Parameters in low Latitudes

4.4. Impact of ELA Depressions on global Climate

4.5. Duration of ice buildup from warm Conditions

4.6. The relief—induced Decay of Glaciers at the End of a Glacial

4.7. Climatically steered Tectonics

4.7.1. Neogene and Pleistocene uplift as in the Holocene

4.7.2. Pronounced uplift since the Holocene

4.8. Tropical Weathering in Tibet and Pre-LGP Interglacials

5. Start and End of warm Climates

5.1. The Panama Seaway

5.2. Orbital Parameters

5.3. Carbon Dioxide

5.4. Effects of Cenozoic High Plateaus

5.5. Impact on the global Energy Budget and Ice Volume

5.6. Impact on the regional Wind Circulation

6. Open Questions, Simulation Design and possible Solutions

6.1. Linking Models and Data

6.2. Future Perspectives

Was this article helpful?

0 0

Post a comment