Climate variability in North America during the past 2,000 years using pollen data
Abstract
The debate concerning the causes of the global temperature increase of the past century results in part from the difficulty in establishing the magnitude of surface temperature change that can be attributed to natural climate variability and that caused by human impact through greenhouse gas emissions. Recent high- resolution paleoclimate reconstructions of the past two millennia using tree-ring and other proxies correlated well in structure and in timing, however, the magnitude of temperature change in these studies divert from one another. This remains a problem that has plagued these studies and the current debate over how much of the recent surface temperature change can be attributed to human impact. We present a new high-resolution summer temperature reconstruction for North America using an extensive network of pollen records. When compared with northern hemispheric temperature anomaly curves based on tree-ring and multi-proxy reconstructions of the past 2,000 years, the results are remarkably similar, in spite of the different methods and proxies employed in these studies. The magnitude of the temperature changes during the Medieval Warm Period and Little Ice Age are comparable to those derived from other proxy records. Regional temperature reconstructions further document the nature of climate changes across North America. Our results show that these recent climate variations between slightly warmer and cooler conditions are part of an ongoing periodic millennial-scale variability that has been operating throughout the Holocene, with irregularly occurring oscillations ~1100 years apart. Quantification of these millennial-scale variations using pollen series are on the order of +/- 0.2°C which is consistent with the climate variations of the past 2,000 years reconstructed using tree-ring series. We hypothesize that the recent warming of ~ +0.6°C of the past century is unprecedented during at least the past 8,000 years.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.U12B..08G
- Keywords:
-
- 0473 Paleoclimatology and paleoceanography (3344;
- 4900);
- 1605 Abrupt/rapid climate change (4901;
- 8408);
- 3344 Paleoclimatology (0473;
- 4900);
- 4914 Continental climate records;
- 4950 Paleoecology