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Hot answers tagged paleoclimatology

79

The IPCC do mentions solar minimums and maximums, as part of extremely careful treatment they do of the reconstructions and predictions for the changes in solar irradiance. The Assessment Report 5, Working Group 1, Chapter 8, have a whole section (~4 pages) dealing with solar irradiances. If the IPCC don't mention grand solar maximums/minumums that often, ...

52

How it's possible to measure temperature 2000 years ago? Sans the technology used by Bill and Ted ("Bill and Ted's Excellent Adventure"), it obviously is not possible to directly measure the temperature from yesterday, let alone 2000 years ago, or longer. What is used are "proxies", things that can be measured today that serve as stand-...

40

I think the main question has already been answered. But I would like to add to the fallacy that: History shows solar activity is the main driver of our climate, among other factors. The Sun is undoubtedly the main source of energy for the planet and its climate. However, variations in solar activity are not the main cause of variations in climate. The ...

28

There has always been a strong north-south rainfall gradient from approximately the Golan Heights (high rainfall), through Judaea and southwards into the arid Sinai desert. We know that this gradient once had a higher rainfall because there are abundant rainfall harvesting and groundwater collection structures, built by the Nabatean civilization about 400 BC ...

25

The Tibetan Plateau uplift is still generally considered as playing a role in the Neogene cooling through the process you explained in your question (see for instance the seminal Zachos et al. 2001 and more recently Garzione 2008). It is probable that other phenomena played a role as well such as the diversification of diatoms (which are, today, the most ...

20

At least four things combined to prevent solid freeze-up during Ice/Slush Ball Earth periods: It takes a lower temperature to freeze water under pressure. Deep sea pressures are enormous. Ice floats. If it sank and new ice kept forming at surface, the seas might fill with ice. The surface freezes first and acts as an approx zero-degree C barrier, ...

19

I think you're slightly confused by some of the terminology. (Caveat: I'm a geophysist, take anything I say with a grain of salt!) We're currently in an interglacial during a prolonged period of icehouse climate (most of the Cenozoic). During most of the Earth's history, the overall climate tends to be much warmer and more stable on the million-year scale....

15

Here is an estimate from Beauchamp and Baud (2002), for parts of the ocean around Pangea, for the latter parts of it's existence (~300-250mya). It is based on various previous papers that looked at deposits of carbonates and phosphate deposits, and made a few assumptions, including a sufficient supply of silica and nutrient inputs, and environments suitable ...

14

What makes you think Geothermal energy and underwater volcanoes are too weak? The mid-oceanic ridge system alone is 50000 miles long. The mean heat flow at the surface (91.6 mW/m2) has to be accommodated somewhere. Also the freezing point of brine at a depth of 5000 m is approx -40 °C.

13

Essentially, we can't. At a meeting some years ago, different specialists tried to define the onset of glaciation and found that each (sub-) discpline had their own definition. An oceanographer boldly stated the glaciation started 2000 years ago since a change in the Greenland ocean currents occurred at that time which was observed to also change before the ...

13

Overall, any individual proxy is not a reliable indicator. It's the combination of multiple proxies that provides a clearer picture. For example, tree ring growth has been correlated with temperatures. However, it's not without it's anomalies: ...from the middle of the 20th century tree ring growth was less than might have been expected from the ...

13

The answer is Volcanos. There might be other inorganic processes capable to produce $\text{CO}_2$, but on Earth, the main inorganic source of $\text{CO}_2$ are volcanoes. In some period of Earth's history, there is evidence of large glaciations events, some of them are thought to have been triggered by the lack of $\text{CO}_2$ (like the Snowball Earth and ...

12

The most accepted theory is that the Younger Dryas was caused by a large reduction or shutdown of the North Atlantic "Conveyor" because of a sudden influx of fresh water from Lake Agassiz and deglaciation in North America. (Although evidence for such an event is thus far lacking.) The global climate would then have become locked into this new state until ...

12

In a word, no. The graph is based on work by Chris Scotese. The climate science site RealClimate.org has this to say about it: Scotese is an expert in reconstructions of continental positions through time and in creating his ‘temperature reconstruction’ he is basically following an old-fashioned idea (best exemplified by Frakes et al’s 1992 textbook) ...

11

One method is through ice cores from the worlds ice caps. Each year, as small amounts of snow accumulate on ice caps such as on Antarctica and Greenland, bubbled of air gets trapped. As we drill through the ice, we can identify the air samples in those trapped bubbles, and measure directly the composition of the air in those bubbled. It tells us much more ...

11

This is a huge and interesting topic. Certainly there are many ways the climate is affected by the lithosphere (and also what is going on in the asthenosphere). The lithosphere is naturally also affected by the climate. I find it difficult to distinguish the 'components' as matter and energy can flow from biosphere to lithosphere and from hydrosphere to ...

11

Fishing through the links mentioned over at Christianity SE, I netted this scientific paper about freshwater and marine fish: Why are there so few fish in the sea?. Apparently the bulk (96%) of marine species have a single freshwater ancestor species extant 300 Mya (300 million years ago). Descendants of this species did not enter the ocean until about 180 ...

10

In addition to the theories mentioned by Azzie Rogers, there is another intriguing (but highly tentative) hypothesis: the YD may have been triggered by a large cosmic impact event. The results of a major study of impact-derived spherules at the time of the YD were recently published by Wittke et al. (2013). I should reiterate, though, that this is not ...

10

I will answer mostly from archaeological perspective; I don't know much about the paleoclimatology before the first people started to produce stone tools. I know just some basics of other disciplines where they affect human (pre)history, but it might help. First, even though longer and older cold periods are also refered as "ice ages", most people don't ...

10

Though I agree with @kaberett that there is indeed more and more evidences that the Deccan volcanism was the main trigger of the K/Pg crisis, i wanted to add that there is a more nuanced hypothesis (that I heard about last week during a talk at EGU) according to which the Chicxulub impact resulting seismic response may be the trigger of one of the main stage ...

10

No, it did not definitively single-handedly cause the KT mass extinction event. Around the same time, the Deccan Traps Large Igneous Province (India) was being emplaced. Flood volcanism has been associated with other mass extinctions, due to the impact on climate, sunlight at the surface, etc, of the output of huge volumes of sulphur-based gases. The ...

10

It seems like you are asking about proxies that are useful on the scale of tens to hundreds of millions of years. We have great proxies that going back thousands of years (tree rings, peat cores, lake sediments), and quite a few that go back around a million or so (speleothem, ice cores), but beyond that the data is in sediments and rocks. Deep sea sediment ...

10

Huh, this is a very interesting question. According to a research paper: The long-term carbon cycle is controlled by chemical weathering, volcanic and metamorphic degassing, and the burial of organic carbon (1, 2). Ancient atmospheric carbon dioxide levels are reflected in the isotopic content of organic carbon (3) and, less directly, strontium (4)...

10

tldr: It was also dry back then, which is why the people living there were rebels and not the rich elite. I'd like to add a few points to Gordon's answer. First of all, Masada is on the western edge of the Judea Desert, and therefore it is dry now and was extremely dry back then. The water supply to it was based on abundant water reservoirs that were built ...

10

Possibly One thing you have to understand is that natural carbon sequestration via the formation of fossil fuel is VERY slow, it can take millions of years to build up the coal we burn in a day. In addition, one of the more dominant effects on the climate is solar radiance and continental position which changes over such long stretches of time, making ...

10

In short: No. Unless multi-million timescales are considered. The reason we keep teaching Newtonian mechanics, is because it is a VERY accurate approximation of a more general theory (general relativity) within the regimes of speed and gravity acceleration found in everyday life. Therefore, all the relativistic corrections to Newtonian mechanics in the ...

8

There is no direct answer. One way to think about this is to consider the water cycle. Water evaporates from the oceans and is precipitates over land. Distance from the ocean affects the amount of precipitation so at the center of a large contintent you may have less precipitation than over a smaller one. Mountains also drain moisture out of the air as it is ...

8

As a preamble, let me say that I don't know remotely enough on galactic dynamic to know if a supernova could have possibly been close enough during the Ordovician for Earth to be affected by a gamma ray burst, nor do I know enough about geochemistry to know if there are ways to detect such an event in the fossil record. That being said, the questions that ...

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