Human Influence on Weather/Climate  Certainties: –We are causing a rapid rise in atmospheric CO 2  Fossil fuel burning  Destruction of forests –Cities are warmer, on average, than their suburbs  Urban Heat Island  Increased emission of heat (cars, people)  Changes in water cycling  Changes in surface area and heat capacity –We have destroyed a significant amount of stratospheric ozone –Higher global temperatures have correlated with increasing CO 2

Caution! Know Your Axes! The perceived slope of a graph means less than you might think! -- Scale of Y-Axis -- Maximum slope with small range -- Minimum slope with large range -- What would graph to left look like if the scale was from 0 to 400? -- Scale of X-Axis -- Same idea- spread it out, decrease the slope Be sure you’re comparing “apples to apples” when looking at more than one graph!

Land Use Changes  The Dust Bowl –Prairie grass was plowed under and overgrazed –With no grass to hold the soil in place, a naturally occurring prolonged dry spell (drought) caused the bare soil to be carried away by the wind; lack of wind breaks (trees)  The Middle East –Biblical reference to the tall cedars of Lebanon –Forests cut down, water cycling changed  Trees/plants retain water, so more runs out of local area  Transpiration: release of water vapor by plants is reduced; water cycle altered

The Urban Heat Island: The Ultimate Land Use Change  Localized climate change: T (city) > T (rural) –Water Cycling: Increased runoff = warmer daytimes (less cooling due to evaporation) –Increased surface area = more solar radiation can be absorbed, more IR emitted and re-absorbed at night; also higher heat capacity building materials building materialsbuilding materials –Autos, factories, people emit heat

Ozone Depletion: Why We Care  Ozone protects us from high-energy (short wavelength) UV radiation from the sun UV radiation UV radiation  Measured in Dobson Units. Decreases in ozone will cause increases in skin cancer, and ozone levels have generally been decreasing. Dobson UnitsdecreasingDobson Unitsdecreasing

Ozone Depletion: Why it’s Happening  Ozone is a highly toxic gas, which means it can be good or bad, depending upon where it is  Good: In the stratosphere, where it protects us from much of the sun’s harmful ultraviolet radiation, which causes skin cancer  Bad: In the troposphere, where we are- it is poisonous!  Chlorofluorocarbons destroy ozone very efficiently

Ozone Depletion: There is Hope  CFCs destroy ozone very efficiently –Destruction greatest in high latitudes –Have been banned and atmospheric CFC levels are leveling off –As atmospheric CFC levels decline, stratospheric ozone should recover, but there is a significant delay between CFC reduction and ozone recovery (~60 years) ozone recovery ozone recovery

Ozone DepletionOzone Depletion: Ozone “Hole” Ozone Depletion  Ozone “hole” is an area over the south pole where stratospheric ozone levels have drastically fallen –Atmospheric conditions (extreme cold, polar vortex) lead to efficient ozone destruction: polar stratospheric clouds (PSC) polar stratospheric clouds (PSC)polar stratospheric clouds (PSC) –Winter/spring occurrence –Not as dramatic over the north pole

A World Avoided… From Douglass, Newman & Solomon, The Antarctic Ozone Hole, an Update

Global Warming: The Enhanced Greenhouse Effect  The Greenhouse Effect keeps our planet about 60F warmer than it otherwise would be. Life as we know it depends upon this effect. Greenhouse gases (primarily water vapor and carbon dioxide) absorb/re- emit IR radiation.  Enhanced Greenhouse Effect is “Global Warming” –Too much of a “good” thing –Anthropogenic (human-induced)  CO 2 : correlates well with temp.  Methane  CFCs – low concentrations, but very efficient IR absorbers

CH 4, CO 2 and Global Temperature Trend

What about cooling I’ve heard about?

Global Decadal Temperatures

Global Warming: Some Uncertainties  Cloud cover: Should increase as condensation nuclei (pollution) increase, but type of cloud has an effect on surface temperature. Some cause cooling, some cause warming. Which type will increase more? Climate models still struggle with cloud prediction.  Sea Level changes: Expected to rise as snow/ice melts, and as water warms (and expands), and is happening now, but some regions will see increased snowfall if planet warms, offsetting some, but not all of the sea level rise –Recent dramatic cooling of top 2,500ft ocean layer Recent dramatic cooling of top 2,500ft ocean layerRecent dramatic cooling of top 2,500ft ocean layer –More recent work on this ocean “cooling” More recent work on this ocean “cooling”More recent work on this ocean “cooling” –Island nations especially concerned  Ocean Currents: Infusion of fresh water alters density, disrupts currents; local climate changes (warming and cooling)  Climate change: Gradual or Rapid? –“slipping” glaciers lubricated by meltwater “slipping” glaciers “slipping” glaciers

Sea Level Rise  Thermal Expansion  Icecaps and Glaciers (Greenland) Greenland

Global Warming: Other Uncertainties  Political Forces –Will countries play by the rules after ratifying a treaty? (Not happening for many countries now) –Should developed countries curtail their emissions and let developing nations continue until their emissions become “substantial?” –Should developing nations be denied the chance the U.S. and other developed nations had?  No, it’s only fair. We can’t stifle their development  Yes, we know more today about what we’re doing to the planet –Then, should developed nations cover the increased cost developing nations will incur to meet stricter environmental guidelines? After all, we screwed it up in the first place. –Carbon credit trading

And Finally…..  And finally, most important of all, basing an economy on a commodity that [in my opinion] is controlled by the most backward, unstable, and violent countries in the world is madness. (2006, but still relevant) - Craig Bohren, in USA Today Craig Bohren, in USA TodayCraig Bohren, in USA Today  Now we have fracking. So, is cheap energy and the potential for energy independence necessarily a good thing?

Key Figures  READ CHAPTER 18, it’s all important