Transcript Basic Climate Slides

Brief Climate Discussion
William F. Ryan
Department of Meteorology The
Pennsylvania State University
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 Temperatures are Rising
Four major recent
independent temperature
studies.
Global Surface Temperature
by Year (dashed) and 5-year Running Average (red line)
There is considerable year-to-year variability in global surface temperature. Warmer
than average years are associated with: El Nino, short term changes in solar output. Cooler
than average years are associated with: La Nina, increased volcanic activity and changes in solar
output. (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
“Natural” Climate Cycles are Driven by
Variations in the Orientation of the Sun and Earth
Solar Input has Changed
Little in Past 30 Years
The Consensus of Climate Models
Can Approximate Past Temperature
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 natural
emissions (blue and blue shading.
Association of Temperature and CO2
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.
Current Temperature Anomaly Likely
Largest in Last 10,000 Years
Marcott, et al., 2013: Science
CO2 Levels are Highest in 400,000 Years
Oceans are Warming Through a Deep Layer
Continuing Rise in Sea Level
Sea Level Rise Amplified Along East Coast
Global Trend in Sea Level Rise Due to
Temperature and Salinity Changes
Milne, et al., 2009: Nature
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.
The Arctic Ice “Death Spiral”
Effect on Northern Hemisphere Weather:
The Arctic Oscillation (AO)
Warmer (less ice volume) Arctic means weaker polar vortex so that cold
air 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 storm
In the southern Plains.
Recent Work on Northern Hemisphere Weather
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?