In a previous post I reported research from Norwegian marine sediment cores and temperature proxies that showed that the current warming period was not only not unusual but also cooler than the Medieval and Roman warming periods.

Reference:

Sejrup, H.P., Haflidason, H. and Andrews, J.T. 2011. A Holocene North Atlantic SST record and regional climate variability. Quaternary Science Reviews 30: 3181-3195.   Abstract here.  Their graph:

A commenter on the previous post dismissed the research saying it was for only one region and did not necessarily represent global temperature history.

Well, here is more research showing that the results found in Norway were similar to results found globally:

Reference:

Bertler, N.A.N., Mayewski, P.A. and Carter, L. 2011. Cold conditions in Antarctica during the Little Ice Age — Implications for abrupt climate change mechanisms. Earth and Planetary Science Letters 308: 41-51.

From ice cores, the researchers were able to identify the temperature differences of the Medieval Warm Period (AD 1140 to 1287), the Little Ice Age (AD 1288 to 1807), and the Modern Era (AD 1808 to 2000). They found “the McMurdo Dry Valleys were 0.35°C warmer during the MWP than now, accompanied by warmer conditions in the Ross Sea.”

Reference:

Liu Y, Cai Q F, Song H M, et al., 2011, Amplitudes, rates, periodicities and causes of temperature variations in the past 2485 years and future trends over the central-eastern Tibetan Plateau. Chinese Sci Bull, 56: 2986 2994, doi: 10.1007/s11434-011-4713-7.

These researchers show that the Medieval Warm period was at least as warm as the current period.  See my post on the paper here.

Reference:

Hu, F.S., Ito, E., Brown, T.A., Curry, B.B. and Engstrom, D.R.  2001.  Pronounced climatic variations in Alaska during the last two millennia.  Proceedings of the National Academy of Sciences, USA 98: 10,552-10,556.

Using sediment cores from Farewell Lake in the northwestern foothills of the Alaska Range, the researchers found that surface water temperatures during the Roman Warm Period and the Medieval Warm Period were the same as those now.

Reference:

Hong, B., Liu, C.-Q., Lin, Q.-H., Yasuyuki, S., Leng, X.-T., Wang, Y., Zhu, Y.-X. and Hong, Y.-T. 2009. Temperature evolution from the ä18O record of Hani peat, Northeast China, in the last 14000 years. Science in China Series D: Earth Sciences 52: 952-964.

Using cores extracted from peat deposits in Northeast China, researchers used oxygen-18 analysis and concluded that the Medieval Warm Period in China peaked about 900 AD and was 1 C warmer than the current warm period.  They also found that “sudden cooling events, such as the Older Dryas, Inter-Allerod, Younger Dryas, and nine ice-rafted debris events of the North Atlantic are almost entirely reiterated in the temperature signals of Hani peat cellulose ä18O.”

Reference:

Millar, C.I., King, J.C., Westfall, R.D., Alden, H.A. and Delany, D.L. 2006. Late Holocene forest dynamics, volcanism, and climate change at Whitewing Mountain and San Joaquin Ridge, Mono County, Sierra Nevada, CA, USA. Quaternary Research 66: 273-287.

Using temperature reconstruction from tree rings, the researchers concluded that the Medieval Warm Period in Nevada was “significantly warmer” (+3.2°C) than present.

Reference:

Kaniewski, D., Van Campo, E., Paulissen, E., Weiss, H., Bakker, J., Rossignol, I. and Van Lerberghe, K. 2011. The medieval climate anomaly and the little Ice Age in coastal Syria inferred from pollen-derived palaeoclimatic patterns. Global and Planetary Change 78: 178-187.

Analyzing pollen contained in sediment cores from alluvial fans, the researchers found evidence that suggests “three peaks centered on ca. 1115, 1130 and 1170 cal yr AD suggest similar or warmer temperatures compared to AD 2000.”

Reference:

Neukom, R., Luterbacher, J., Villalba, R., Kuttel, M., Frank, D., Jones, P.D., Grosjean, M., Wanner, H., Aravena, J.-C., Black, D.E., Christie, D.A., D’Arrigo, R., Lara, A., Morales, M., Soliz-Gamboa, C., Srur, A., Urritia, R. and von Gunten, L. 2011. Multiproxy summer and winter surface air temperature field reconstructions for southern South America covering the past centuries. Climate Dynamics 37: 35-51.

Using multiple temperature proxies, the researchers concluded the warmest decade of this Medieval Warm Period in Southern South America was AD 1079-1088, and that was about 0.17°C warmer than the peak warmth of the current warm period.

Reference:

Holmgren, K., Tyson, P.D., Moberg, A. and Svanered, O.  2001.  A preliminary 3000-year regional temperature reconstruction for South Africa.  South African Journal of Science 97: 49-51.

These researchers deduced temperature variations from stalagmites in caves.  They estimate that the Little Ice Age between AD 1500 and 1800, was about 1°C colder than they are presently.  During the Medieval Warm Period at around AD 900 temperatures reached 2.5°C higher than at present.  Another exceptionally warm period was noted in the late fifteenth century, when temperatures rose more than 3°C above the current level.

The foregoing gives just a few examples showing that climate is cyclical and current temperatures are not unusual.  There is still no credible evidence that I am aware of that supports the contention that our carbon dioxide emissions are the major cause of recent warming.  For another overview see here.

In the current warm period, temperatures are increasingly artifacts of poor station siting that creates a warming bias (see Surfacestations.org) In a study of U.S. stations it was found that “9 of every 10 stations are likely reporting higher or rising temperatures because they are badly sited.”  Part of the problem is that many stations are in or near growing cities and suffer from the Urban Heat Island effect, i.e., during the day, the sun heats concrete and asphalt which then radiate heat at night making temperatures in the cities (and at the stations) warmer than rural areas.  And, there is also the problem of data manipulation by government agencies with an agenda.

For some additional perspective, the graph below shows global temperature as measured from satellites, beginning in 1979.  Although atmospheric carbon dioxide has been increasing, there does not seem to be a corresponding temperature response.  In the graph, temperatures before the strong El Nino event in 1998 show no trend.  Temperatures after 1998 also show no trend.  The difference is temperature levels before and after is attributed to shifts in global atmospheric cycles such as the Pacific Decadal Oscillation and El Nino.

Researchers from the University of Bergen and the University of Colorado studied marine sediment cores from the Norwegian continental margin.  They were able to get accurate dates from lead isotope dating of interspersed volcanic rocks in the core.  They examined oxygen-18 isotopes from the calcium carbonate in the shells of planktonic foraminifera to reconstruct temperature. (Oxygen-18 is a proxy for temperature, see NASA’s Earth Observatory explanation of the method here.)

This allowed the researchers to come up with what they call “”near surface water summer temperature.” for the past 2,000 years.  The following graph depicts their temperature reconstruction:

The graph shows that the current warm period is cooler than the Medieval and Roman warm periods.  The researchers report a statistically significant correlation with the Gleissberg solar cycle.  This is more evidence that the forces of natural variability overcome the effect, if any, of anthropogenic carbon dioxide emissions, and it shows that current warming is neither unprecedented nor unusual.

Reference:

Sejrup, H.P., Haflidason, H. and Andrews, J.T. 2011. A Holocene North Atlantic SST record and regional climate variability. Quaternary Science Reviews 30: 3181-3195.   Abstract here.

A strange thing has been happening to the historic temperature dataset.  NOAA/NCDC have been frequently revising the temperatures, and not just for recent data, but for temperatures going all the way back to 1880.  The folks at C3Headlines have been keeping track of temperature data sets for several years.  They noticed that NOAA has been revising the dataset almost monthly, and noted that there were six revisions in December and three so far in January.  The revisions have a particular pattern.  Temperatures from dates before 1940 are being gradually made cooler, while temperatures since 1951 are being made warmer.  The effect is to make recent warming seem more alarming.  Other agencies that keep temperature data sets rarely make revisions.  See the story from C3Headlines here.