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Global warm-up not seen in last 1,400 years

COLUMBIA (US) — Earth’s climate warmed more between 1971 and 2000 than during any other three-decade interval in the last 1,400 years.

Experts base the finding on new regional temperature reconstructions covering all seven continents.

This period of manmade global warming, which continues today, reversed a natural cooling trend that lasted several hundred years, according to results published in the journal Nature Geoscience by 78 scientists from 24 nations analyzing climate data from tree rings, pollen, cave formations, ice cores, lake and ocean sediments, and historical records from around the world.


A year-by-year analysis reveals that Europe, in 2003, had the hottest summer in more than 2000 years. (Credit: dolanh/Flickr)

“This paper tells us what we already knew, except in a better, more comprehensive fashion,” said study co-author Edward Cook, a tree-ring scientist at Lamont-Doherty Earth Observatory at Columbia University, who led the Asia reconstruction.

The study’s reconstruction of European temperatures also provides context for the 2003 heat wave and drought that killed an estimated 70,000 people across Europe. A year-by-year analysis reveals that Europe, in 2003, had the hottest summer in more than 2000 years.

“Summer temperatures were intense that year and accompanied by a lack of rain and very dry soil conditions over much of Europe,” says study co-author Jason Smerdon, a climate scientist at Lamont-Doherty and one of the lead contributors to the Europe reconstruction.

Though summer 2003 set a record for Europe, global warming was only one of the factors that contributed to the temperature conditions that summer, he says.

The study is the latest to show that the Medieval Warm Period, from about 950 to 1250, may not have been global, and may not have happened at the same time in places that did grow warmer.

While parts of Europe and North America were fairly warm between 950 and 1250, South America stayed relatively cold, the study says. Some people have argued that the natural warming that occurred during the medieval ages is happening today, and that humans are not responsible for modern day global warming.

Scientists are nearly unanimous in their disagreement.

“If we went into another Medieval Warm Period again that extra warmth would be added on top of warming from greenhouse gases,” says Cook.

Global trend

Temperatures varied less between continents in the same hemisphere than between hemispheres.

“Distinctive periods, such as the Medieval Warm Period or the Little Ice Age stand out, but do not show a globally uniform pattern,” says co-author Heinz Wanner, a scientist at the University of Bern, in a press release.

By 1500, temperatures dropped below the long-term average everywhere, though colder temperatures emerged several decades earlier in the Arctic, Europe, and Asia.

The most consistent trend across all regions in the last 2,000 years was a long-term cooling, likely caused by a rise in volcanic activity, decrease in solar irradiance, changes in land-surface vegetation, and slow variations in Earth’s orbit.

With the exception of Antarctica, cooling tapered off at the end of the 19th century, with the onset of industrialization. Cooler 30-year periods between 830 and 1910 were particularly pronounced during weak solar activity and strong tropical volcanic eruptions.

Both phenomena often occurred simultaneously and led to a drop in the average temperature during five distinct 30- to 90-year intervals between 1251 and 1820.

Warming in the 20th century was on average twice as large in the northern continents as it was in the Southern Hemisphere. During the past 2,000 years, some regions experienced warmer 30-year intervals than during the late 20th century. For example, in Europe the years between 21 and 80 AD were likely warmer than the period 1971-2000.

The study involved the collaboration of researchers in China, Pakistan, India, Russia, and the US, among others, under the auspices of the International Geosphere-Biosphere Programme. The project, Past Global Changes 2k Network, or PAGES 2k Network, was funded by the US and Swiss National Science Foundations and the National Oceanic and Atmospheric Administration. The data compiled in the study will be made public and incorporated into the 2013-2014 climate report by the Intergovernmental Panel on Climate Change.

Source: Columbia University

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4 Comments

  1. Joseph Blumberg

    A very deceptive headline!

  2. russ george

    The writer in his zeal to oppose has skipped some of his reading assignments. Indeed the role of CO2 is at the root of the issue, or rather the leaf of the issue. Where I agree is with the idea that climate modellers have gone totally overboard with their narrowly defined models. Yes CO2 acts indirectly as a greenhouse gas but its far more potent and direct action is as a plant nutrient.

    Our high and rising CO2 is dramatically changing plant ecosystems everywhere and those plant ecosystems are changing the world. In just this past month a pivotal paper in the Journal Nature by a grad student in New Mexico has revealed the epic power of CO2.

    As plants benefit from our high CO2 world they are working less and thus losing less water via transpiration (breathing). As is reported in the Nature paper plant transpiration provides 4-5 times more water vapour to the air than does evaporation!

    Water vapour is the most important “greenhouse gas” many times the potency of CO2. Plants are now putting in dramatically less of their primary greenhouse gas (water vapour) as they remove ever more CO2 from the air. Here’s a link to read more http://russgeorge.net/2013/04/23/high-co2-terrestrial-plant-growth-reduction-of-global-warming/

    More important however is that plants can be helped to remove even more CO2 from the air, billions of tonnes of dangerous CO2 can be turned into life itself. The cost of replenishing and restoring plant life to manage these billions of tonnes of CO2 is mere millions not billions of dollars…It’s Ecoengineeging, giving something back to Nature so that we may continue to recieve…read how here http://russgeorge.net/2013/04/28/a-call-to-100-villages/

    Join us. Choose Life. IT JUST WORKS!

  3. nerf herder

    That’s interesting Russ, and you have a nice website. It’s nice to see science-based claims that aren’t the usual skeptic’s claims of conspiracy and “models can’t be trusted”, etc. And yes, water vapor overpowers CO2 as a global warming gas, but it’s hard to measure trends in water vapor since it varies daily and seasonally so much.

    However, I’ve read in the past that increased CO2 doesn’t really increase plant growth all that much, certainly not at a one-to-one ratio (it has a muted effect). Add to that, the increased acreage that is put into monoculture fields that don’t have the amount of plant growth a full forest or prairie would have. Corn in particular, tends to require a lot of water, and I’ve heard that makes the summers in the U.S. Midwest more humid than they used to be. So as the population of the world continues to increase, would new fields counter the effect of less transpiration among existing plant life? It’s still indisputable that CO2 levels have risen over the last 150 years, and so have temperatures. Your point would seem to say that’s not happening.

    I’ve also read that fossil fuel usage is only about 40% of the release of CO2 since the age of industrialization – most of it actually comes from plowing under the prairies, cutting the forests, and planting crops which are only present seasonally, and bare dirt for much of the year, releasing its stores of sequestered CO2.

    So maybe more efficient cars aren’t the cure-all, but more drought-resistant crops and better farming techniques (including lab-grown meat!) are.

  4. Anechidna

    There are a lot of drivers to climate variability that we understand only poorly. For instance during 2012 the British Met Office seeking to improve their predicative capacity for the large low pressure instense cold storms that were appearing literally our of nowhere. Discovered that by monitoring the stratosphere to 80km instead of 50km the cause of these events. They have termed it SSW (Sudden Stratospheric Warming) where the upper stratosphere would heat up over a few days by up to 50C, they do not know the cause of the sudden warming as of yet. But this suddenly warmed air mass then blocked the normal path of the cold weather lows at lower altitudes causing them to track further south than they normally would.

    Now CO2 levels are not responsible for this sudden warming and the sun has not yet been implicated in this heating but something heats the upper stratosphere.

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