Brief Climate Discussion

William F. RyanDepartment 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 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

“Natural” Climate Cycles are Driven byVariations in the Orientation of the Sun and Earth

Solar Input has ChangedLittle in Past 30 Years

The Consensus of Climate ModelsCan 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 naturalemissions (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 LikelyLargest 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 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.

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?