Last month, we reported on the umpteenth study that confirmed the Hockey Stick. It made clear the rate of global warming since 1900 is 50 times greater than the rate of cooling in the previous 5000 years.
That study, Marcott et al, is the most the most comprehensive “Reconstruction of Regional and Global Temperature for the Past 11,300 Years” ever done. It’s the source of most of the data (in blue) in the jaw-dropping graph at the right (click to enlarge). Projected warming this century (in red) on humanity’s current emissions path comes from the recent literature.
Now a team of 78 researchers (from 60 institutions) in the international network PAGES (PAst Global Changes) has “published the most comprehensive reconstruction of past temperature changes at the continental scale” over the past 2000 years. Their Nature Geoscience article (subs. req’d) concludes:
The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between AD 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period AD 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.
No “worldwide Medieval Warm Period or Little Ice Age.” Another denier myth bites the dust.
Here is a key figure from the new study:
Standardized 30-year-mean temperatures averaged across all seven continental-scale regions. Blue symbols are area-weighted averages, and bars show 25th and 75th unweighted percentiles to illustrate the variability among regions; open black boxes are medians. The red line is the 30-year-average annual global temperature from the HadCRUT4 instrumental time series relative to 1961–1990, and scaled visually to match the standardized values over the instrumental period.
As you can see, the 30-year mean temperature is already at the highest level in almost 1400 years, and this is just the 1971–2000 average. The 1982–2010 average is higher yet again on this scale.
And so we have the hockey stick, which countless studies have now vindicated — though as the top chart makes clear, within a few decades the hockey stick will soon look more (and feel more) like a brick wall.
You can find everything you could want to know about the new study, “Continental-scale temperature variability during the last two millennia,” at the PAGES website. Here are the “primary conclusions” from the FAQ:
(1) The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the 19th century.
– The regional rate of cooling varied between about 0.1 and 0.3°C per 1000 years.
– A preliminary analysis using a climate model indicates that the overall cooling was caused by a combination of decreased solar irradiance and increased volcanic activity, as well as changes in land cover and slow changes in the Earth’s orbit. The simulations show that the relative importance of each factor differs between regions.
(2) Temperatures did not fluctuate uniformly among all regions at multi-decadal to centennial scales. For example, there were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age.
– The period from around 830 to 1100 CE generally encompassed a sustained warm interval in all four Northern Hemisphere regions. In contrast, in South America and Australasia, a sustained warm period occurred later, from around 1160 to 1370 CE.
– The transition to colder regional climates between 1200 and 1500 CE is evident earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere.
– By around 1580 CE all regions except Antarctica entered a protracted, multi-centennial cold period, which prevailed until late in the 19th century.
– Cooler 30-year periods between the years 830 and 1910 CE were particularly pronounced during times of weak solar activity and strong tropical volcanic eruptions. Both phenomena often occurred simultaneously. This demonstrates how temperature changes over large regions are related to changes in climate-forcing mechanisms. Future climate can be expected to respond to such forcings in similar ways.
(3) The 20th century ranked as the warmest or nearly the warmest century in all regions except Antarctica. During the last 30-year period in the reconstructions (1971–2000 CE), the average reconstructed temperature among all of the regions was likely higher than anytime in nearly 1400 years. However, some regions experienced 30-year intervals that were warmer than 1971–2000. In Europe, for example, the average temperature between 21 and 80 CE was warmer than during 1971–2000.
Skeptical Science has a good post on the study here.
- NOAA (2013): ‘Robust, Unambiguous’ Independent Evidence Confirms The Recent Global Warming Measured By Thermometers.