Polar Amplification of Climate Polar Amplification of Climate

Polar Amplification of Climate

Polar Amplification of Climate Change in Coupled Models Holland, M. M. , Bitz, C. M. Climate Dynamics, Vol. 21, Issue 3 -4, pp. 221 -232, Sept 2003. n n Analysis of northern hemisphere polar amplification of climate by means of comparison amongst a group of climate models Surface warming in the arctic Magnitude n Distribution n Seasonality n

Sea-ice physics for models with high polar amplification

Whats going on with BRMC?

Variables n Sea ice Extent n Thickness n n Snow coverage on land Cloud coverage Ocean heat transport

Sea Ice Extent n n Ice extent and latitude of maximum warming are significantly correlated, R=-. 80 Models with larger ice extents have a tendency to have maximum warming at lower latitudes, why is this?

Sea Ice Extent n n Larger ice extents generally cause higher global sensitivity because the earth has more available ice to melt (only for models with low-moderate polar amplification) why not high amplification models? No significant correlation between ice extent and normalized warming, considering all models together

Sea Ice Thickness n More highly correlated to normalized warming than sea ice extent, R=-. 40

Sea Ice Thickness n n n Suggests that because thin ice is more easily melted, warming causes greater loss of ice extent Greater albedo feedback and loss of insulation between ocean and atmosphere amplify the warming Still, weak correlations suggest some other factors may be at work. . .

Snow Coverage on Land n n No significant correlation between snow coverage and normalized warming, considering all models together However, as with ice extent, a significant correlation exists among the models with lowmoderate polar amplification, R=. 67

Snow Coverage n Correlation (among low-moderate amplification models) is probably a result of the snow coverage on land being highly correlated to the extent of ice, and not indicative of the snow extent influencing the polar amplification of warming

Cloud coverage n Does increased cloud coverage have a positive or negative effect on polar amplification of warming?

Cloud Coverage – Temperature Feedbacks High Clouds Temperature Cloud coverage Absorbed solar radiation at surface Low Clouds Temperature Cloud coverage Absorbed solar radiation at surface

Summer Clouds n n Changes in icealbedo, and thus absorbed solar radiation, did not result in changes in cloud cover during summer However, the high amplification models do have a tendency to have increased summer cloud cover

Winter Clouds n n n Also, decreased winter cloud cover in control climate is correlated to higher polar amplification, R=-. 50 Problem: model bias? Control climate cloud conditions related to change in clouds, R= -. 76, Lower levels of original cloud cover allow for greater change Larger winter cloud cover changes correlated to higher amplification, R=. 74,

Cloud Coverage n Problems: No distinction between high and low clouds n Don’t know enough about cloud relationships and feedbacks n Don’t have data from all of the models n

Ocean Heat Transport

ECH-3 CCSM CERF MRI BMRC CCSR CCC GFDL-A GISS

ECH-3 BMRC MRI CCSM CCSR GFDL-A CERF CCC GISS

Ocean Heat Transport n Control climate ocean heat transport and change in transport are both significantly correlated to polar warming

Ocean Heat Transport n Because increased heat transport by the ocean is correlated with both sea ice extent and thickness, it seems possible that this then decreases surface albedo by melting sea ice and amplifies warming

Conclusion n Possible factors affecting increased polar amplification based on these models: Thin sea-ice cover n Increased ocean heat transport to poles n Increase in winter cloud cover n

Conclusion n n Further work is needed within single models to clarify and better understand the relationships suggested by this group of models From this study it is clear that very accurate depictions of current sea ice characteristics, such as extent and thickness, are necessary to receive valid data concerning the arctic responses to increased warming by greenhouse gases

Arctic pictures