Determining the Local Implications of Global Warming Clifford Mass University of Washington

Global Warming 101

The Earth With No Atmosphere (infrared) Earth’s surface would be 60F cooler than today…no life.

But the Earth has an atmosphere! Includes gases such as nitrogen and oxygen Also includes greenhouse gases.

What is a Greenhouse Gas? Greenhouse gas is a gas that that is relatively transparent to solar radiation, but absorbs and emits in the infrared…the type of radiation the earth emits. Some examples: Water vapor Carbon dioxide Nitrous oxide Methane

Earth With An Atmosphere That Includes Greenhouse Gases Partly (infrared) Greenhouse Gases Make the Earth Warmer by Slowing the Loss of Infrared Radiation

Greenhouse Gases Warm the Earth in a Similar Way That Blankets Warm Us at Night

The Problem: Rapidly Rising Greenhouse Gases Due to Mankind

Gases Trapped in Ice Gives Us a History of the Gases in the Atmosphere

But it is worse than that… There are a number of natural “amplifiers” of mankind’s emission of greenhouse gases. The warming due to increased carbon dioxide, methane, and other greenhouse gases will cause more water to be evaporated from the earth’s oceans.

Amplifier The amount of evaporation increases with temperature. Water vapor is the most potent greenhouse gas and thus causes even MORE warming. This produces a positive feedback.

But it gets even worse… Warming temperatures melt snow and ice. Snow and ice help cool the planet because they reflect much of the sun’s radiation….that is why you need sun glasses while skiing. As the snow melts less radiation is reflected to space and more is absorbed. Thus, the earth gets warmer, which melts more snow. Another positive feedback!

Is Global Warming Already Happening? Finding the global warming signal is made more difficult because the earth’s climate has a certain amount of natural variability. Also the warming due to man was relatively small before the middle of last century before the large increase in fossil fuel usage. The consensus of most atmospheric scientists is that some global warming signal due to man is now evident.

Eleven of the twelve warmest years in the past 150 years have occurred in the past twelve years (1995-2006)

But Not All “Signs” of Global Warming Are Due to Mankind

These photographs, taken in 1928 and 2000, show how South Cascade Glacier in the Washington Cascade Mountains has retreated over time. BUT…this melting began prior to the period when mankind could have had much of an impact. Represents the end of the Little Ice Age.

But what about the future?

The Technology of Prediction Atmospheric scientists use complex climate prediction models…called General Circulation Models…GCMS…to predict the future climate. These models are similar to weather forecast models, but allow the gases in the atmosphere to change. They also simulate the evolution of the oceans. Have to assume the future emission of greenhouse gases by mankind…call scenarios..a major uncertainty. These models are not perfect and cannot exactly replicate the current climate….but they are close and getting better each year.

Details on Current Study: GCM Which Scenario Will Mankind Follow? IPCC Report, 2001 IPCC Report, 2001

IPCC.AR4.2007 FIGURE SPM-5. Solid lines are multi-model global averages of surface warming (relative to 1980-99) for the scenarios A2, A1B and B1, shown as continuations of the 20th century simulations. Shading denotes the plus/minus one standard deviation range of individual model annual averages. The orange line is for the experiment where concentrations were held constant at year 2000 values. The gray bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios. The assessment of the best estimate and likely ranges in the gray bars includes the AOGCMs in the left part of the figure, as well as results from a hierarchy of independent models and observational constraints. {Figures 10.4 and 10.29}

Sample Climate Model Output for 2100

What about the Northwest? Several of us are applying very high resolution simulations forced by the global climate model predictions Gives a view of the local implications of global warming. Could our mountains and other local features make it worse or better?

Northwest weather is dominated by terrain and land-water contrasts of much smaller scale. In order to understand the implications of global changes on our weather, we must consider our local terrain and land use.

Running High Resolution Regional Climate Models 135, 45, 15 km MM5 domains Need 15 km grid spacing to model local weather features.

Snow and Ice Reflect Much of The Incoming Solar Radiation

Global Warming Causes Snow level to Rise Resulting In Absorption of Solar Energy on Melted Slopes Solar Radiation Future =WARMING

Why Relative Cooling West of Cascades in Spring? Low clouds due to more onshore flow from off the cool, cloud Pacific. The Montereyization of the western lowlands!

Large Drop in Snowpack in the Mountains

Key Facts The overwhelming majority of atmospheric scientists believe global warming forced by mankind’s changes to the atmosphere has occurred and will became MUCH larger during the next decade. This is based on the best technology and observations available. There are substantial uncertainties, so we can’t give a specific number, but a range. Even if increases in the emission of greenhouse gases stop today, a certain amount of global warming is inevitable.

Range of Global Warming

Global Warming Goes Political and Reaches the Public Arena

Inconvenient Truth: Basically Accurate But Contains Some Errors

Downplays Global Warming: Full of Major Errors

Mayor Nickels and Global Warming Claims of a 50% reduction in Cascade snowpack due to global warming are simply not true. Perhaps 10-15%

Little Change In Snowpack Over the Last 30 Years

More flooding and heavy rains under global warming? Not necessarily if the jet stream moves northward.

Bottom Line Global warming and its local implications are very serious. There are significant uncertainties, but they are NOT in whether global warming will occur, but rather the magnitude and its local effects.

The End