Brief Climate Discussion William F. Ryan Department of Meteorology The Pennsylvania State University
Dec 22, 2015
Summary of Remarks
• Global temperatures are rising.– Arguments to contrary have no scientific basis.– The rate of rise may be unprecedented.
• This rise cannot be attributed to “natural” causes.– Little change in solar output in last 30 years– We are in a static, slightly cooling portion of the earth-solar cycle.
• Climate models can accurately reproduce the historic global temperature record.– But only if man-made emissions are included.
• Current climate impacts are, as predicted, most noticeable in the the Arctic.– Loss of Arctic ice and strongest rate of warming.
• “Breaking” Science: – Changes in land-based Greenland ice.– Increasing variability in Northern Hemisphere weather patterns.– Variations in strength of Gulf Stream – impacts sea level along East Coast.
Global Surface Temperatureby Year (dashed) and 5-year Running Average (red line)
There is considerable year-to-year variability in global surface temperature. Warmerthan average years are associated with: El Nino, short term changes in solar output. Coolerthan average years are associated with: La Nina, increased volcanic activity and changes in solaroutput. (See, this Short Film for a clever explanation)
“No Recent Warming” Talking Point is a Fallacy:Selective truncation (“cherry picking”) of a time series of data can
show any 10-year period has a cooling trend
Every year since 2000 has been warmer than the mean temperature of the 1990’s.
Twelve of the warmest thirteen years have occurred Since 2000.
Another interesting short film: 16 Year Film
Models “Work” Only if Anthropogenic Greenhouse Gas Emissions are Included
Observed global temperature anomaly (black line), consensus of climate models(red) and range (pink shading), consensus of climate models with only naturalemissions (blue and blue shading.
Recent Research
• Several extensions of the time series of temperature into deep past.– Wider set of ice core data.
• Recent ocean temperature data.• Longer term CO2 concentrations• Impact of melting Arctic on Northern
Hemisphere weather patterns.
Arctic Melting: Positive Feedback Cycle
Melting sea ice leads to less reflection of sunlight, warmer temperatures,more melting sea ice and warming of the ocean.
Effect on Northern Hemisphere Weather:The Arctic Oscillation (AO)
Warmer (less ice volume) Arctic means weaker polar vortex so that coldair can “leak” southward.
Reduced Strength of Polar Vortex:Likely to Lead to More Erratic Weather?
Example from May 3, 2013
Amplified Surges of Arctic air
Unusual early May snow stormIn the southern Plains.
Areas of Concern for East Coast of US
• Sea Level Rise:– Rate of Loss of Greenland Land-Based Ice Melt?
• Significant Impact on Sea Level Rise.
– Weakening of Atlantic Meridional Overturning Currents • Gulf Stream is one branch.• Atlantic Coast from HAT to Cape Cod may see locally higher
sea level rise.
• Warmer Ocean– Extension of hurricane season?– Impact on ENSO?