CE 401Climate Change Science and Engineering

Climate Change Science (in one lecture)

13 January 2011

homework 2: use the Mauna Loa data on the class website to graph the annual averageincrease/decrease in atmospheric CO2 (in %) from 1959 to 2009. Read Chapter 1 of Houghton.Due Thursday, 1/20

note – as this talk on climate science procedes:• be skeptical• look hard at the data

• ask questions !!!!!!!!!!!!!!!!• don’t be misled• the debate is polarizing and political• the implications of action are controversial and expensive

Revelle and Suess (1957): “human beings are now carrying outa large scale geophysical experiment of a kind that could nothave happened in the past nor be reproduced in the future. Within a few centuries we are returning to the atmosphere and oceans the concentrated organic carbon stored in sedimentary rocks over hundreds of millions of years”

Outline• introduction

• greenhouse gases and Earth temperature

• evidence for climate change in the past

• evidence for current climate change

• climate change, policy makers, and climate models

• predicted effects of climate change

• some thoughts on global energy usage

temperature structure of the Earth’s atmosphere

composition of the Earth’s atmosphere

solar and earth spectra

Greenhouse Gases

• H2O - by far most important GHG - ~ 60% of total GH effect

• CO2 - 70% of human produced GHG effect• e.g., an automobile with 20 mpg fuel economy produces ~ one pound CO2 per mile --> 7 tons/yr at 15K miles/year• preindustrial conc. = 260 ppm, current conc. 390 ppm• mostly produced by industrial/transportation sectors

• CH4 - methane 25% of human GHG effect• preindustrial conc. = 0.7 ppm, current conc. 1.7 ppm• biomass burning, landfills, animal/human waste

• N2O - nitrous oxide 5% of human GHG effect• cultivated soils, industrial, biomass burning, feedlots

Thursday, 13 January

• questions from last time???

• overview of climate change science

HW #2:• use the Mauna Loa CO2 data on the class website to graph the annual averageincrease/decrease in atmospheric CO2 (in %) from 1959 to 2009. Show all your workand state your assumptions

• Read Chapter 1 of Houghton

Due Thursday, 1/20

Greenhouse Gases (GHG) and Energy Balance

• GHG transmits light (energy) well in the visible part of the spectrumwhere the Sun (Teff ~ 5700K) produces most of its energy

• GHG is relatively opaque in the infrared part of the spectrum wherethe Earth radiates most of its energy (10µm ~300K)

• this “blanket” of gases insulates the Earth• the radiation coming in from the Sun must still be radiated out the Earth reaches a higher equilibrium temperature than w/o GHG• Earth is ~ 33°C warmer than w/o the atmosphere

solar spectrum to 3µm

Global Change due to Human Influence is a Reality

• air and water pollution• burning of fossil fuels

• industrial activity• transportation• electrical generation

• changing land use• vegetation• urbanization• desertification• biomass burning• wetland destruction

Weather and Climate

• weather occurs over a relatively short time scale (days, weeks, months)

• climate is the average weather over years, decades, centuries

• causes and effects of climate change are generally in the troposphere, the bottom 10 km of the atmosphere

CO2 increases are clearly human induced and are acceleratingcurrent increase is about 1.9 ppm/year (not subtle)

CO2: pre-industrial : 280 parts per million; current: 392 ppm; 38% change in 50 years

What Processes Control Atmospheric CO2?

• Only ~ half of the CO2 produced by human activities remains in the atmosphere

• CO2 is not reactiveand lives a long time in the atmosphere

• where are the sinks of CO2 - ocean, forest, …?

Evidence for Climate Change in past

not human induced

The atmospheric concentration of CO2, N2O, and CH4 now exceeds by far the natural range of the last 650,000 years - currentchanges have occurred all in a few hundreds of years

CO2

CH4

N2O

600 0time (thousands of years before present)

360

200

note

Current level ishigher than anytime in past 600,000 years.

150,000 years ago to present

this graph dramatic evidence that CO2 drives climate: more CO2 higher temperatures. YES?

Here is Al Gore on this graph: “Here is an important point. If my classmate from 6th grade were to seethis, he would ask, “Did they ever fit together?”. The answer from the scientist would be, “Yes, they dofit together.”. It’s a complicated relationship, but the most important part of it is this: When there ismore CO2 in the atmosphere, the temperature increases because more heat from the sun is trappedinside. There is not a single part of this graph – no fact, no date, or number – that is controversialin any way or is disputed by anyone.”

What is cause and effect? The implication here, honestly stated by Gore, but implied, is more CO2 , higher T

Yet, many scientists think the opposite: large changes in CO2 were a result of the warming, not the cause. Changes in temperature in this graph weredriven not primarily by CO2 changes, but by changes in the orbit and axis of the Earth.

Caillon et al, 2003, Science 299, 1728 CO2 lags behind temperature changes by about800 years + 200 years (why 800 years?)

Some climate scientists now doubt the order. Richard Muller (Physics for Future Presidents, 2008) “The fairest statement that can be made is that the issue is unsettled”. “Many people see the plot and come away believing that CO2 has been established as the main driver for past climate change. That is very likely a correct conclusion for small (1°C) changes attributed to the present CO2 increase, but not clear for the dramatic temperature variations of ancient data shown in the plot”

source: Jouzel et al. 1994

10°C

10°C

5°C

age (thousands of years ago)0150

Antarctica

Greenland

North Atlantic

Antarctic and Greenland Ice Core and N. Atlantic Sed. Temp. Data

note how stable temperature has been for the last 10,000 yrs

HOCKEY STICK PLOT

Mann et al, 1998

hockey stick:• published in 1998• NH remarkably constant showing cool years 1000-1900 with significant global warming occurred• 2001 IPCC report included it – 5 times in the summary volume alone• prominently featured in Al Gore’s film• showed the modern fossil fuel era was unprecedented in increased temperature• just like the CO2 rise plot patently obvious that humans were causing warming• Canadian gov’t sent a copy to every household in Canada• every politician in DC was familiar with it• 14th century COLD period appears nowhere in the plot (it was European only?), but that cold period

is well established• the graph is wrong – the analysis has proved to be faulty and really only representswestern US, not the northern hemisphere

• US National Academy of Sciences was asked by Congress to review confirmation of error• does it matter that the hockey stick plot was wrong?

• yes, it reinforces misconceptions• to a scientist, it is wrong, but it is just another step in the process• IPCC consensus did not depend on the hockey stick graph of temperature vs time• it is embarrassing for sure

• scientists usually reach the truth, but sometimes it takes a while

CO2 concentrations are increasing due to industrial activity

CO2 Concentrations (ppm) 1860 - 1995

the sun and climate

Solar variability and late 20th-century Warming

satellite measurements of solar brightness

0.1% variation

natural variations in climate are caused by (at least):

• changes in the radiation balance of the Earth-Sun system• intrinsic changes in solar flux

• long term - must be modeled using sunspot numbers• solar cycle - only two cycles measured + 0.05%

• changes in Earth orbital parameters - Milankovitch cycles• periods of 20k - 100k years• explain all the major ice ages – dramatic changes in temperature

• changing aerosol concentrations (e.g. volcanic activity)

Conclusions from the Climate Record preindustrial to 650k years ago (no human influence)

• temperatures have varied by approximately 7°C

• highest observed CO2 is about 300 ppmv (current 385 ppmv)

• highest observed methane is about 0.7 ppmv (current 1.7 ppmv)

• temperature, CO2 and methane follow each other closely in time

• changes have generally occurred over long time periods• past 10K years have been remarkably stable in temperature

• this period marked the development of civilization• most “equable” climate of the past many millions of years

• rapid (decadal) changes in surface temps of 5-6°C have

occurred in the past

Evidence for Current Climate Change

US surface temperature record

Global Mean Temperatures

Annual meanSmoothed series5-95 decadal error bars

source: IPCC = source: IPCC = Intergovernmental Panel on Climate Change, 2007Intergovernmental Panel on Climate Change, 2007

11 of the past 12 years are the hottest on record

• last decade is the warmest decade on record• increase in past 25 years is ~ 0.2°C/decade

NASA Global Temperature Record 1880 - 2008

source: GISS, 2010

NOAA (12 JAN 2011) 2010 tied 2005 as the hottest year on record

detection of significant change is a statistical problem:

• finding a small signal in a sea of poorly understood noise• the instrumental record is short --> rely on proxy measurements• changes have obviously occurred over the past 100 years that are

not human related• 1920 - 1943 warming• 1970s cooling

• if an observed change in the record is judged unlikely to have occurred due to natural processes --> implicates human factors (???)• assignment of attribution to a human cause requires consideration

and elimination of all plausible non-human mechanisms• can’t eliminate all plausible mechanisms

• cause and effect are usually approached with a series of controlled experiments, but this cannot be done in this case

• experiment is not systematic - too many parameters are being changed at one time

What are some of the problems with these graphs of

surface temperature vs time?

There are lots of problems with these graphs!!

What are possible problems?????

urban heat island effect

California surface weather stations

Robinson et al (2007): Surface temperature trends 1940-1996 from 107 measuring stations in 49 CA counties. Trends combined for counties of similar population. The “X” show the stations used by NASA GISS for their estimate of global surface temperatures. Suchselections make the NASA GISS modeled temperatures too high.original source: F. Singer, Hot Talk, Cold Science, 1997

California weather stations

• where is temperature data collected (geographic distribution)

• how is temperature collected? (same method everywhere?)

• what affects the reading of the thermometer? (surroundings)

• consistency of measurement method over a period of years

sea surface temperature 1850 - 2004

source: IPCC 2007 what are potential problems with this graph?

red = observations

models

red: reconstructed sea level fields since 1870 (Church and White, 2006)blue: coastal tide measurements since 1950 (Holgate/Woodworth 2004)black: satellite altimetry (Leudiette et al, 2004)

sea level change 1880 - 2004

source: IPCC 2007

Figure 5.1

0-700m layer. shading = 90% confidence.

Global ocean heat content

source: IPCC 2007

Snow cover and Arctic sea ice are decreasing (area vs time)

Spring snow cover in millions of square km1920 - present

Arctic sea ice area decreased by 2.7% per decade

1979 - 2005

source: IPCC, 2007

glaciers are retreating

Figure 4.22variations in monthly areal extent of seasonally frozen ground for1901 - 2002 in NH, smoothed

source: IPCC 2007

POLICY MAKERS ARE INTERESTED IN THEFUTURE

What will happen and what is the cause?

Models are used to predict future climate

How well do these models predict the past?

Can we trust models to predict the future?

Decisions are based on the models!

source: IPCC 2007 The Climate System - very complicated

What Goes into Atmospheric Climate Models

• mathematical equations to describe air motion and processes• solar flux and its changes in time - Earth energy balance• clouds - largest source of uncertainty in the models

• 61% of the globe on average is covered with clouds• clouds both reflect energy (cooling)• and serve as thermal blankets (warming)

• Earth reflectivity (land, sea/water, ice, snow, vegetation, etc.)• thermodynamics of water and radiation• chemistry and carbon cycle (atmosphere, oceans, biosphere)

• anthropogenic contributions (e.g. CO2 increases with time,

biomass burning, land use changes, etc.)• aerosols which cool the atmosphere (natural and anthropogenic)

The atmospheric models must be coupled to:

• cryosphere• biosphere• oceans• hydrosphere

• all on a high resolution global spatial grid of latitude and longitude and altitude as a function of time and incorporating the many feedback mechanisms that control atmospheric processes

This is a huge job that requires experts from many fields and a large computer! There are a number of groups around the world working on this problem.

Observations

Natural + Human-induced

With human-induced influenceWith human-induced influence

Observations and Model ComparisonTemperature Change, 1900 - Present

Natural

Without human-induced influenceWithout human-induced influence

black = observations red = modeled natural + human blue = modeled natural alone

IPCC 2007

The Current Scientific Consensus (remember that science is not about

consensus)

IPCC, 2007:

“the observed widespread warming of theatmosphere and ocean, together with icemass loss, support the conclusion thatit is extremely unlikely that global climatechange of the past 50 years can be explainedwithout external [human] forcing, and verylikely that it is not due to known naturalcauses alone.”

Projected changes in annual temperatures for the 2050s

The projected change in annual temperatures for the 2050s compared with the present day, when the climate model is driven with an increase in greenhouse gas concentrations equivalent to about 1% increase per year in CO2

BW 11

source: GISS

-30%-10 0 10+30%

South Florida: 1-m rise in Sea Level

Change in January Average Daily Maximum Temperature (doubling of CO2)

source: Hotchkiss and Stone (2000)

Present

CO2 doubling

by 2050

Vegetation Changes for Modeled Doubling of Carbon Dioxide

source: IPCC, 1996

Temperate forests

Grasslands

Deserts

Savanna

Tropical seasonalforest

Tropical moistforest

Ice

Tundra

Boreal forests

Color Code: now

x 2 CO2

Global Energy Useage

• industrialized nations• 20% of population• 75% of carbon emitted since 1950• ~< 50% of today’s carbon emissions

• developing nations• 80% of population• 25% of carbon emissions since 1950• ~> 50% of today’s emissions• economic & population growth --> huge emissions increases

country on lower axis – which one is the US?

toe per capita

1971 - 2003 by region; mtoe = million tonnes of oil equivalent

summary:

• GHG concentrations are increasing without any doubt whatsoever – it is not subtle• the cause of the GHG increase is clearly human caused• there is little debate that climate warming is occurring• the debate centers on the causes of the debate – is it natural or human-caused

• the Earth climate system is very complicated• the science is never complete and there will always be intelligent questions• climate is difficult to model and make predictions, but the models are what we have• the majority of models predict significant changes in average Earth temperature

• the rhetoric is polarizing• the politics is loud and divisive• should policies be put in place to limit the growth of GHG? These policies will

radically change fossil fuel combustion as a source of energy

• what can engineers contribute to the changes that will be coming?