Lv 7
Trevor asked in EnvironmentGlobal Warming · 9 years ago

How does the current warming compare to past warming events?

Earth’s atmospheric temperature is never static and throughout history there have been significant warming and cooling events. In the distant past the planet has been frozen solid whilst at other times palm trees have grown in the polar regions and there’s been no ice anywhere. Then of course there’s the ‘ice-ages’ that come and going approximately once every 100,000 years.

A thousand years ago Earth’s temperature peaked during the Medieval Warm Period it then spent the next 700 years cooling as we entered the Little Ice Age.

All these changes, and more, relate to variations in the amount of total solar irradiance (energy from the Sun) that we receive.

In the last 100 years or so, how much has the planet warmed in comparison to any of the natural variations? What is total solar irradiance doing now – is it increasing, decreasing or staying the same?

Please keep your answer relevant and provide actual figures. Example: in the last X years Earth has warmed by Y°C, in the same period during such and such an event it warmed by Z°C.

9 Answers

  • gcnp58
    Lv 7
    9 years ago
    Favorite Answer

    The only thing that comes close to the recent warming in terms of temperature rise per decade might be the PETM (although that warming rate was perhaps an order of magnitude lower than what has been observed over the last 150 years). Similarly, interstadial eras take thousands of years to form (and the timescales for glaciation is tens of thousands of years). The MWP had not the temporal geographical coherence of the recent warming, nor was the temperature rise as large so the temporal temperature gradient is consistent with numbers from the PETM or deglaciation.

    This "order of magnitude" difference between the rate of warming in the anthropocene and anything found in the paleo record is why you claim the warming is unprecedented. You are not wrong and there is not a shred of evidence to say the warming in the modern era is caused by internal climate variability. As far as our understanding of the physics goes, it could only be the result of radiative forcing from anthropogenic CO2.

    Edit: If you take an ice core data record and compute temperature changes over a running 200-yr interval (approx. the length of the anthropocene), you will find that less than 3% of the time there are periods with temperature increases that are as large as the anthropocene. And that is for a deglaciation when global mean temperature is increasing. During interstadials or ice ages, when temperature is far more constant, there are no times when the gradient is as large. It is wildly improbable from a statistical standpoint that the temperature increase during the anthropocene in natural variability. Any claim to the contrary is simply irrational. It is the same as asserting that because there could be a type of energy reaching the planet we don't know about that is causing the warming (this cannot be proven to be false, although it is wildly unlikely), there is no reasonable basis for concern that anthropogenic CO2 is affecting climate.

    Ok, here's a histogram of the temperature warming rates during the collapse of the second to last ice age from about 140,000 Yrs B.P. to 125,000 Yrs. B.P.

    Temperature gradients were computed over a fixed number of data points so it's a little biased towards longer intervals as ice age increases, but then there are more intervals at the beginning so it kind of averages out. What this shows is that the temperature increase during a deglaciation is greater than the anthropocene gradient less than 2% of the time (and that's for deglaciation, and we are not in that mode right now (we're in an interstadial)). Using this data to argue that temperature rise at the end of an ice age looked similar at times to what is going on now shows a colossal lack of understanding of physics and statistics.

    Source(s): PETM warming: +6 C in 20,000 years 0.0003 C/yr Interstadial: +9C in 12,000 years 0.00075 C/yr Anthropocene: +0.8 C in 150 years 0.005 C/yr These numbers can all be found with short google searches.
  • 9 years ago

    I think I get a much better feel for what's going on by tracking heat and phase changes than by trying to make sense of the extremely noisy temperature records.

    The previous low stand of the oceans was about 120 meters below present sealevel about 22 kiloyears ago. Considering average depth of the ocean, that means approximately 1/30 of the ocean which was stored on land as ice melted and flowed back into the ocean. The heat required to accomplish this averages out to about 1/3 watt per square meter during those 22kyears. The same amount of heat would raise ocean temperatures about 10 kelvins. The IPCC 4th report estimates our present anthropogenic heat retention at 1.6 w/m2.

    Edit - oops, forgot unit conversion in ocean temp rise equivalence. Should be 2.5 kelvins.

  • bob326
    Lv 5
    9 years ago

    I don't have much time, but his is a good question. I've noticed in several of your recent answers, Trevor, that you state that the current global warming is "unprecedented" over some incredible timeframe (eg 500My), and I plainly don't agree that such a statement can be made. Over the past several millennia, the rate over the past century appears to be unprecedented, but even this cannot be said with a high level of confidence. On a global scale, the spatial and temporal resolution of available proxy records are simply not high enough to say with much certainty that a particular century within the last 15ky did NOT warm at a comparable rate to today. As we go further back, concrete statements about centurial scale warming become even more difficult.

    And the fact is that we do NOT have a true global reconstruction which extends beyond a few millennia, and any older reconstructions are at best quasi-global built out of a few, often disparate, incompatible and unreliable, proxy records.

    Paleoclimatology is a fascinating and incredibly important field of study, but I think most experts in the field would agree that statements about relatively short term warming rates (eg a century) in the proxy records are uncertain at best. Average warming over several millennia are more certain, but not by a great deal.

    However, as I've noted before, whether the current warming is unprecedented or not in no way precludes it from being anthropogenic in origin, or from being potentially dangerous if emissions remain unabated.

  • John
    Lv 5
    9 years ago

    We are in a pretty normal time, except for all of the alarmists who want us to believe them.

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  • 9 years ago

    There is evidence that there was an extremely rapid warming event (several degrees in just a few decades) at the end of the Younger Dryas. The important difference is that this rapid warming came after a very cold period lasting for around 1000 years where the average temperate was around 5C. The warming was essentially returning the temperature to equilibrium (~14C), whereas the current warming trend appears to be a warming above the equilibrium baseline.

    So in the last 50 years earth has warmed by ~0.5C, while insolation has declined and sunspot number has varied. In the same period 11Kya the earth warmed by ~9C but insolation and sunspot data is not available.

    Source(s): Alley et al (1993). Abrupt increase in Greenland snow accumulation at the end of the Younger Dryas event. Nature, Volume 362, Issue 6420, pp. 527-529
  • 9 years ago

    Over the past 100-150 years we have several different temperature data sets (based on a myriad of other more regional data sets). There are many different proxies, there are various thermometer readings from populated areas, there's "bucket" reading from ships (SST), now there's satellites and ocean buoys and probably still quite a few I haven't mentioned.

    As I understand it, to get an accurate analysis of what some call a "global surface temperature average" there needs to be quite a bit of data homogenization and adjustments made. We rarely have any single type of measurement (i.e. data set) which has truly global coverage (expect for satellites now). That means we need to extrapolate, interpolate, discard some data, account for urbanization, account for station relocations, account for missing data, make sure the data has the proper metadata, etc. And adjustments to entire datasets happen on a regular basis as we learn more (e.g. the new HadCRUT4 data series).

    And frankly, all data sets don't agree exactly for various reasons, measurement error being one or differences of analysis being another.

    If you take all that about what we know and can measure about the Earth's average temperature (in past 100-150 years), how exactly are we supposed to know with anything that could be considered with useful accuracy about global temperatures 500, 1000, 10000, 100000 years ago? For example, in one Climategate email Keith Briffa remarked: "I know there is pressure to present a nice tidy story as regards 'apparent unprecedented warming in a thousand years or more in the proxy data' but in reality the situation is not quite so simple." And the word "pressure" has its own implications but I won't go there.

    As far as solar activity, I'll just say that total solar irradiance is but one of many metrics of the Sun's activity out of several that may affect the Earth's climate. Solar variations include total solar irradiance, ultraviolet irradiance, solar wind, magnetic flux, solar field, solar particles, solar proton events, mass coronal ejections, etc.

    And then we need to look at the different solar cycles and the periodicity of those cycles.

    11 years - Scwabe Cycle (basis sunspot cycle)

    22 years - Hale Cycle (inversion of Sun poles)

    87 years - Gleissberg cycle

    210 years - Suess cycle

    2,300 years - Hallstatt cycle

    And then there's the work of Theodor Landscheidt who pioneered work in what is know as "solar inertial motion" which may explain some of the above cycles by the gravitational pull of the planets on the Sun causing the Sun to change its barycentre. His work is being carried on by several solar physicists including Nicola Scafetta who has published many peer reviewed studies. Here is his latest:

    So when I hear the statement: "The warming in the past 50 years is unprecedented and cannot be explained by any natural forcing therefore CO2 is the responsible for most of the warming in recent years", I see two or three things in that claim that are dubious at best and completely unsupported at worst.


    Edit: Just reading over some of the climategate emails, I found this:

    Chick Keller to Mann, Jones, Briffa, et al: "...many careful scientists will decide the issue is still unsettled and that indeed climate in the past may well have varied as much or more than in the last hundred years."


    Edit@Gringo: "3) the rate of average global temperature changes during past warming events. In the past it took a thousand years for the earth to warm 1 degree Celsius. Currently, we are observing a warming of 0.7 degree Celsius in the past 100 years alone. The implications of such a rapid warming also escape many (and not only those who do not believe in evolution):"

    Ironically, the error in your above statement escapes you. Perhaps Trevor can correct you but I'll give you a clue: decadal and multi-decadal time frames.


    Edit2@Gringo: "Perhaps you better contact NASA asap because they state the exact same thing in the link I provided."

    I don't doubt that all you did was parrot some authoritative source and your link shows that. You still didn't show any independent critical thinking by asking yourself (or NASA for that matter) what temperature changes can occur over decadal or multi-decadal time frames regardless of a long term trend.

    Source(s): Please really think about this. Here is the NASA quote: "...the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years. In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly ten times faster than the average rate of ice-age-recovery warming." This statement is assuming that within those 5000 years, there was never a 100 year period where temperatures rose by 0.7C. Do you not have single skeptical, scientific bone in your body? Do you simply accept what is written because it's NASA?
  • Gringo
    Lv 6
    9 years ago

    <<In the distant past the planet has been frozen solid whilst at other times palm trees have grown in the polar regions and there’s been no ice anywhere. Then of course there’s the ‘ice-ages’ that come and going approximately once every 100,000 years.>>

    This is precisely a core issue which many fail to grasp, as a result of which they cannot comprehend the fundamental differences between past warming episodes and today's. It has three parts:

    1) Many erroneously believe that a) during ice ages the whole of the earth was covered in ice and b) the period in earth's long history that it was solidly frozen was an ice age when in fact it was not. Large parts of the world did in fact have above freezing temperatures during so called ice ages. See this artist's impression of what the world looked like during an ice age:

    2) the relatively little average global temperature difference between ice ages and warmer periods in between (aka interglacials). Many wrongly assume there are huge temperature differences between ice ages and interglacials which could explain why they believe that the current observed warming is not significant. See

    3) the rate of average global temperature changes during past warming events. In the past it took a thousand years for the earth to warm 1 degree Celsius. Currently, we are observing a warming of 0.7 degree Celsius in the past 100 years alone. The implications of such a rapid warming also escape many (and not only those who do not believe in evolution): the ability of earth's inhabitants (animals, plants, humans) to adopt to their changing environment coupled with the inability to comprehend just how much we humans depend on that (ie, for food), even when they're living in a comfortable air conditioned home in some elegant suburb.

    At this stage, after decades of global investigation, not only has human carbon dioxide been found to be the culprit via multiple methods and lines of investigation, any other cause or causes for the observed warming have been extensively researched and found not to be responsable. Despite that, the usual denier scientists and their blog-based peers continue to beat those dead horses.

    So I for one am looking forward to some thorough, well researched answers here by what might be this century's Einstein which blows the current scientific theory of global warming completely out of the water.

    More info below (highly recommended for those who fall into the above 3 point category).

    Edit @ Ottawa Mike:

    <<Ironically, the error in your above statement escapes you. Perhaps Trevor can correct you but I'll give you a clue: decadal and multi-decadal time frames.>>

    Perhaps you better contact NASA asap because they state the exact same thing in the link I provided.

  • 9 years ago

    Not nearly as significant as past events

  • 9 years ago

    This is a good question, and since nobody here knows the answer better than you, I will simply guess off the top of my head without doing the slightest research that current climate change (CO2 change, temperature change, icecap meltoff, ocean acidification, extreme weather events, etc.) is hundreds or thousands of times faster than "normal" variation in the past, and probably several times faster than all but a handful of very outlying "natural catastrophes" (massive volcano outbreaks, huge asteroid impacts, etc.) across the last few billion years.

    EDIT: John Rockford's answer (just prior to this one), suggesting that past (natural) episodes of global climage change were more significant than current AGW, offers substantiation by linking to an article, written by a PR man with no apparent credentials in climate science, and posted on, a bucket-shop quality blogosphere infotainment outlet

    The two-year old article uses statements by fake scientists to pretend that Phil Jones, in a BBC interview, supports the dubious hypothesis that the "Medieval Warming" episode was comparable in significance and global scope to present-day warming. The BBC article is linked to, so anyone with an open mind can readily see how Jones' actual statements are deliberately misconstrued in examiner's anti-science polemic. But, of course, deniers and dupes at whom the article is targeted being the OPPOSITE of skeptics, they will swallow such anti-science koolaid without bothering to even look closely at it.

    The fake scientists quoted or referenced in the Examiner piece include Phil Kotzbach a supposed researcher at the Atmospheric Sciences Dept at Colo. St (but not listed on their website), Tim Ball, a non-scientist hired gun of fossil fuel companies who periodically pretends to be a "climatologist," and a kook blogger with little or no evident knowledge of science For its grand finale, the article concludes by quoting an anonymous poster to the blog WattsUP, run by a college dropout whose expertise at cutting and pasting far exceeds any competency in actual science.

    I bother to recount this tip of the con artistry iceberg example in order to ask, Trevor, what makes you think your rhetorical questions (such as this one) will be in any way effective against such a massive ignorance- and conspiracy-theory worshipping disinformation bandwagon ?

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