Study of 11,300 years of weather suggests record warming ahead
By Monte Morin, Los Angeles Times
March 7, 2013, 2:01 p.m.
First the good news: In the last 11,300 years, humans have endured a planet warmer than today's, even as they set about building their earliest civilizations.
Now the bad news: That will no longer be true 87 years from now, according to scientists who have conducted a comprehensive analysis of the planet's climate history since the world's ice sheets began their most recent retreat from North America and Europe.
New research into the Earth's ancient climate is providing a clearer, more detailed view of how the planet's average surface temperature fluctuated over the period known as the Holocene epoch, which continues through to the present day. It's the time in which humans truly began making their mark on the planet, abandoning their hunting and gathering traditions and adopting a settled, agricultural lifestyle.
In a study being published in Friday's edition of the journal Science, researchers used eight indirect temperature indicators — such as pollen and shells from marine organisms — to chart long-term global warming and cooling trends. The research team concluded that temperatures in the last decade have not exceeded the Holocene's steamiest periods from thousands of years ago. However, if current warming trends hold, those records will be broken by the end of the century.
"By the year 2100, we will be beyond anything human society has ever experienced," said study leader Shaun Marcott, a post-doctoral researcher at Oregon State University's College of Earth, Ocean and Atmospheric Sciences.
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http://www.latimes.com/news/science/la-sci-climate-warming-20130308,0,1220004.story
= new reply since forum marked as read
...I found an interesting blog by Andrew Revkin in the New York Times Opinion Pages: Scientists Find an Abrupt Warm Jog After a Very Long Cooling. Revkin includes a couple of videos of Skype conversations with one of the authors of the paper. He also contacted two other climate scientists, Michael Mann and Robert Rohde, to get their views of the new results and includes transcripts from those conversations.
He summarizes the results:
A new Science paper includes this graph of data
providing clues to past global temperature.
It shows the warming as the last ice age ended (left),
a period when temperatures were warmer than today,
a cooling starting 5,000 years ago and
an abrupt warming in the last 100 years.
A quote from Micheal Mann:
My only real concern is that their data and approach (e.g. the use of pollen records in the higher northern latitudes) seems to emphasize the higher latitudes of the Northern Hemisphere, during the summer season. This is an issue because we know there is a substantial long-term natural cooling trend for high-latitude summers because of Earth orbital effects, but the trend is nearly zero in the global annual average. One gets the sense from looking at their reconstruction that there is a very strong imprint of this orbital cooling trend — stronger than what one would expect for the global annual average.
The interesting thing about that, is that it suggests that the true conclusions might even be stronger than their already quite strong conclusions, regarding the unprecedented nature of recent warming. That is, it may be that you have to go even further back in time to find warmth comparable — at the global scale — to what we are seeing today. If you look at their tropical stack for example (Figure 2J) [a particular set of data], the modern warmth is unprecedented for the entire time period (i.e, the past 11,000 years). That’s why I said that there results suggests recent warmth unprecedented for at least the past 4,000. It’s possible, given the potential seasonality/latitudinal bias, that there is in fact no precedent over the past 11,000 years (and likely longer, since the preceding glacial period was almost certainly globally cooler than the Holocene) for the warmth we are seeing today. In that case, we likely have to go back to the last interglacial, i.e. the Eemian period (125,000 years ago) for warmth potentially rivaling that of today.
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and something from Robert Rohde:
Because the analysis method and sparse data used in this study will tend to blur out most century-scale changes, we can’t use the analysis of Marcott et al. to draw any firm conclusions about how unique the rapid changes of the twentieth century are compared to the previous 10,000 years. The 20th century may have had uniquely rapid warming, but we would need higher resolution data to draw that conclusion with any certainty. Similarly, one should be careful in comparing recent decades to early parts of their reconstruction, as one can easily fall into the trap of comparing a single year or decade to what is essentially an average of centuries. To their credit Marcott et al. do recognize and address the issue of suppressed high frequency variability at a number of places in their paper.
<snip>
The whole discussion is a good read.
BTW: What's a kardashian?
