date: Mon, 31 Jul 2006 14:09:01 +0100 from: "Quaternary Science Reviews" subject: Reviewer Invitation for JQSR-D-06-00143 to: Ms. Ref. No.: JQSR-D-06-00143 Title: On the 'Divergence Problem' in Northern Forests: A Review of the Tree-Ring Evidence and Possible Causes Quaternary Science Reviews Dear Prof Keith Briffa, You are invited to review the above-mentioned manuscript that has been submitted for publication in Quaternary Science Reviews. The abstract is attached below. Are you available to provide the review? PLEASE DO NOT USE YOUR E-MAIL "REPLY" OPTION TO RESPOND TO THIS INVITATION. Instead, please respond online at http://ees.elsevier.com/jqsr/. You will need to login as a Reviewer: Your username is: KBriffa-255 Your password is: briffa5873 Please select the "New Invitations" link on your Main Menu, then choose to "Accept" or "Decline" this invitation, as appropriate. If you accept this invitation, I would be very grateful if you would return your review by Sep 11, 2006. You may submit your comments online at the above URL. There you will find spaces for confidential comments to the editor, comments for the author and a report form to be completed. To assist you in the reviewing process, I am delighted to offer you full access to Scopus* for 30 days. With Scopus you can search for related articles, references and papers by the same author. You may also use Scopus for your own purposes at any time during the 30-day period. If you already use Scopus at your institute, having this 30 day full access means that you will also be able to access Scopus from home. Access instructions will follow once you have accepted this invitation to review *Scopus is the world's largest abstract and citation database of research information and quality internet sources. With kind regards, Claude Hillaire-Marcel Editor Quaternary Science Reviews ABSTRACT: An anomalous reduction in forest growth and temperature sensitivity has been detected in tree-ring width and density records from many circumpolar northern latitude sites since around the middle 20th century. This phenomenon, also known as the "divergence problem", is expressed as an offset between warmer instrumental temperatures and their underestimation in reconstruction models based on tree rings. The divergence problem has significant implications for large-scale patterns of forest growth, the global carbon cycle, and the development of paleoclimatic reconstructions based on tree-ring records from northern forests. Herein we review the current literature that has been published on the divergence problem to date, and assess its possible causes and implications. The causes, however, are not well understood and are difficult to test due to the existence of a number of covarying environmental factors that may potentially impact recent tree growth. These possible causes include temperature-induced drought stress, nonlinear thresholds or time-dependent responses to recent warming, delayed snowmelt and related changes in seasonality, and differential growth response to maximum, minimum and mean temperatures. Another possible cause of the divergence that is proposed herein is 'global dimming', a phenomenon that has appeared, in recent decades, to decrease the amount of solar radiation available for photosynthesis and plant growth on a large scale. Increased dimming is due to globally increasing concentrations of air pollution that reduce the transparency of the atmosphere and affect cloud properties. It is theorized that the dimming phenomenon should have a relatively greater impact on tree growth at higher northern latitudes, which is consistent with what has been observed from the tree-ring record. Additional potential causes include "end effect" problems that can emerge in standardization and chronology development, and biases in instrumental target data and its modeling. Although limited evidence suggests that the divergence is anthropogenic in nature and restricted to the recent decades of the 20th century, more research is needed to confirm these observations. ****************************************** For any technical queries about using EES, please contact Elsevier Reviewer Support at reviewersupport@elsevier.com