On 18 April 2012, very recently, a major study was published:
The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability, by B. Christiansen and F. C. Ljungqvist, Climate of the Past, 8, 765–786, 2012
Download it and check it out for yourself!
Don't be afraid. The truth won't bite you!
This is what the study concluded:
We have compiled a set of 91 temperature sensitive proxies located in the extra-tropical NH that reach back to at least 1500 AD. All the proxies have been published in the peer reviewed literature. Of these proxies, 32 extend as far back as to the beginning of the first millennium. From these comprehensive proxy compilations we performed new reconstructions of the extra-tropical Northern Hemisphere mean temperature.
Note, however, that only little more than half of the proxies (the exact fraction depends on the calibration interval, etc.) correlate well enough with the local annual mean temperature to be included in the actual reconstructions.
The reconstructions are carried out with the LOCal (LOC) method (Christiansen, 2011), which was designed to preserve low-frequency variability at the price of exaggerating the high-frequency variability. The LOC method accomplishes this by obtaining local temperature reconstructions using linear regression, with temperature as the independent variable. This corresponds to a forward model which is the physical sound choice. The local reconstructions are then combined to a reconstruction of the extra-tropical NH mean temperature by simple averaging, thereby avoiding the complications of more complex spatial covariance models.
Confidence intervals have been calculated with an ensemble pseudo-proxy approach which mimics the conditions of our real-world reconstructions, including the spatial and temporal averaging. These calculations indicate that the extra-tropical NH mean reconstructions have only a small bias.
The corresponding 95 % confidence intervals have widths of 0.6 (two-millennia long reconstruction) and 0.4'C (500-yr long reconstruction) for 50-yr smoothed values, thereby showing that the residual noise-variance is relatively small compared to the reconstructed low-frequency signal.
Our main conclusions are as follows.
– Our reconstructions indicate – in agreement with the results of Moberg et al. (2005); Ljungqvist (2010), and Loehle and McCulloch (2008) – that the first millennium AD was generally significantly warmer than the second millennium AD. The 17th century was the coldest century during the last two millennia and most of the Little Ice Age (LIA) seems to have been colder than during the Dark Age Cold Period ca. 300–800 AD. In general, our LOC reconstructions show larger low-frequency variability than previous reconstructions.
– Our two-millennia long reconstruction has a well-defined peak in the period 950–1050 AD with a maximum temperature anomaly of 0.6°C. The timing of the peak of the Medieval Warm Period (MWP) in our reconstruction is in agreement with the reconstructions of Esper et al. (2002a) and Ljungqvist (2010). The reconstructions of Mann et al. (2008, 2009) show a longer peak warming covering the whole period 950–1100 AD, and the re-construction of Moberg et al. (2005) shows a somewhat later as well as longer peak MWP warming than in the present paper. The level of warmth during the peak of the MWP in the second half of the 10th century, equalling or slightly exceeding the mid-20th century warming, is in agreement with the results from other more recent large-scale multi-proxy temperature reconstructions by Moberg et al. (2005), Mann et al. (2008, 2009), Ljungqvist (2010), and Ljungqvist et al. (2012).
– Temperatures in the 17th century reach values as cold as -1.0°C below the 1880–1960AD level, in agreement with a previous LOC reconstruction by Christiansen and Ljungqvist (2011) based on fewer proxies. We find that this result is very robust relative to the calibration period and the number of proxies included. This level of cooling is considerably colder than obtained with other reconstruction methods (see also Christiansen and Ljungqvist (2011) for additional comparison). In the 19th century temperature anomalies reach values of ca. —0.9 degree C, but this value is some-what more sensitive to the calibration period. The two temperature minima are separated by a local maximum in the 18th century. This temporal variation of the temperature throughout the LIA is in line with most previous work. Most regional to global multi-proxy temperature reconstructions studies agree that the 17th century was the coldest century during the LIA (Ljungqvist, 2010; Ljungqvist et al., 2012; Hegerl et al., 2007; Mann et al., 2008, 2009; Moberg et al., 2005; National Research Council, 2006), although high-latitude summer temperatures seem to have reached a minimum in the 19th century (Grudd, 2008; Kaufman et al., 2009; Ran et al., 2011; Vinther et al., 2010; Sicre et al., 2011). The maximum cooling in the 17th century is also supported by General Circulation Models and Energy Balance Models (Ammann et al., 2007; Friend, 2011; Gonz´alez-Rouco et al., 2006; Jungclaus et al., 2010; Servonnat et al., 2010; Hofer et al., 2011; Swingedouw et al., 2011) using state-of-the-art estimates of past radiative forcing. The 18th century is generally found to be warmer than both the 17th and the 19th centuries with, regionally, temperatures as high as in the mid-20th century.
– We find that the LIA is spatially homogeneous with cold anomalies everywhere and almost the same patterns in the 17th and the 19th centuries. The homogeneity of the LIA is in agreement with previous work (Juckes et al., 2007; Matthews and Briffa, 2005; National Research Council, 2006; Wanner et al., 2008, 2011; Ljungqvist et al., 2012). The MWP seems more inhomogeneous, as has also been suggested in several previous studies, including Bradley et al. (2003), Hughes and Diaz (1994), Diaz et al. (2011) and Mann et al. (2009). However, we find that the statistical significance is low due to the limited number of proxies, in agreement with Esper and Frank (2009) who suggested that the use of relatively few noisy and poorly replicated proxies can give a false impression of heterogeneity. Ljungqvist et al. (2012) show that, on centennial time-scales, the MWP is no less homogeneous than the LIA if all available proxy evidence, including low-resolution records, are taken into consideration in order to give a better spatial data coverage.
– The large number of proxies allow us to compare LOC reconstruction based on different number of proxies and thereby test the influence of the spatial averaging. Re-constructions based on 16 to 55 proxies (after screening) show only small differences in 50-yr smoothed temperatures that generally fall inside the 95 % confidence interval calculated by the ensemble pseudo-proxy method. This suggests that low-frequency noise is a minor problem and that LOC reconstructs 50-yr smoothed extra-tropical NH mean temperatures well.
And here's the key chart (click for larger image):
What does this mean?
1. It means that there has been A PERIOD EXACTLY AS WARM AS TODAY, ABOUT ONE THOUSAND YEARS AGO.
2. It means that there WAS a Little Ice Age from which the world is currently recovering. The recovery started WELL BEFORE man made CO2 emissions became significant (which happened only after 1950, and that too, only a little bit: most "man-made" CO2 has been emitted only after 1990).
3. There is no correlation between CO2 and temperature. We have seen this clearly earlier today.
It means that there is NO WAY THAT ANY SENSIBLE STATISTICIAN can conclude that there is evidence of MAN MADE warming. Fools are of course welcome to their delusional conclusions. (Some of these fools are PROFESSORS! Student beware for you can be easily taken for a ride by fool professors. Remove your blinkers. Ask HARD questions.)
Note I'm NOT saying that CO2 is not a greenhouse gas. It can and DOES warm. But then it is offset by negative feedbacks. That's the key point that "scientists" have not even remotely understood. They are crying wolf not on the basis of DATA but on the basis of a theory.
They might as well say that Santa is angry with mankind. Same thing. Pure theory. No data.
To conclude: there is SIGNIFICANT EVIDENCE that climate changes by itself due to natural causes.
There is NO evidence that CO2 is bad.
There is ONLY evidence that CO2 is good (for plants).
So don't worry. Be happy.
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