Most of the the tree ring studies are showing that we have been cooling and are temps are below previous warm periods. This is important because the warming nutters liked to take the tree ring data and then graft instrument records on the end of it... to act like we are warming. my theory is that is baloney. you can't take proxy records and act like they are just like a thermometer. Proxies may be used for reference but not for exact temps. Proof? the proxy records don't which continue on to modern times... show cooler temps than the instrument data. Why... could be the adjustments to the instrument data are wrong. Could be that the proxies are correct. Could be the standard for the proxies was set a bit low. Anticipated argument... Some will argue these are just records for north america or limited places. Response... the nutters use the same proxy data in their charts... they just cut off the recent decades. We use tree rings and ice cores to recreate the temps.
note how the red lines (instrument data) in the graph below... compares with the proxy data. its significantly higher. http://www.nature.com/nclimate/journal/v2/n12/full/nclimate1589.html Orbital forcing of tree-ring data Jan Esper, David C. Frank, Mauri Timonen, Eduardo Zorita, Rob J. S. Wilson, Jürg Luterbacher, Steffen Holzkämper, Nils Fischer, Sebastian Wagner, Daniel Nievergelt, Anne Verstege & Ulf Büntgen Nature Climate Change (2012) doi:10.1038/nclimate1589 Received 27 March 2012 Accepted 15 May 2012 Published online 08 July 2012 1, are an important driver of Holocene climate2, 3. The forcing is substantial over the past 2,000 years, up to four times as large as the 1.6 W m−2 net anthropogenic forcing since 1750 (ref. 4), but the trend varies considerably over time, space and with season5. Using numerous high-latitude proxy records, slow orbital changes have recently been shown6 to gradually force boreal summer temperature cooling over the common era. Here, we present new evidence based on maximum latewood density data from northern Scandinavia, indicating that this cooling trend was stronger (−0.31 °C per 1,000 years, ±0.03 °C) than previously reported, and demonstrate that this signature is missing in published tree-ring proxy records. The long-term trend now revealed in maximum latewood density data is in line with coupled general circulation models7, 8 indicating albedo-driven feedback mechanisms and substantial summer cooling over the past two millennia in northern boreal and Arctic latitudes. These findings, together with the missing orbital signature in published dendrochronological records, suggest that large-scale near-surface air-temperature reconstructions9, 10, 11, 12, 13 relying on tree-ring data may underestimate pre-instrumental temperatures including warmth during Medieval and Roman times. a, The reconstruction extends back to 138 BC highlighting extreme cool and warm summers (blue curve), cool and warm periods on decadal to centennial scales (black curve, 100-year spline filter) and a long-term cooling trend (dashed red curve; linear regression fit to the reconstruction over the 138 BC–AD 1900 period). Estimation of uncertainty of the reconstruction (grey area) integrates the validation standard error (±2 × root mean square error) and bootstrap confidence estimates. b, Regression of the MXD chronology (blue curve) against JJA temperatures (red curve) over the 1876–2006 common period. Correlations between MXD and instrumental data are 0.77 (full period), 0.78 (1876–1941 period), and 0.75 (1942–2006 period).
I probably would have questioned how much impact such a small component of the atmosphere could have and I still do. I know that the agw nutter, for a while, answered this question by saying that co2's "forcing" was magnified by water vapor or clouds... but further studies have shown that clouds may contribute to cooling... So the point is... science is working on it but the earth's systems are dynamic and complex. In short we don't know what adding man made co2 is doing.