20th Century Climate Change Data, Causation

Current Climate Change: Data and Causes

• This is how I’ll group the slides in this presentation:

• A. Global Temperatures

• B. Sea Level Changes

• C. Arctic Ocean Ice

• D. Glacier Retreats

• E. Permafrost and methane

A. Global Temperatures

• Temperature rise in the Industrial Age in the context of the past: recent and geologic time scales

The Global Temperature Record for the past ~150 Years Can Be Roughly Divided into 4 Regimes

1. Up to ~1912

• Human generated GHG’s are still fairly small. Cars are a rarity, human population is a small fraction of today’s.

• We are still in the general regime of the past interglacial ~6000 years, which shows little trend in global temperatures

• However, an unusually large number of major volcanic eruptions added significant cooling stratospheric aerosols: Krakatoa 1883 (climatically strongest in modern record, see especially Gleckler et.al. 2006), Santa Maria (1902, one of the 5 biggest of the past 200 years), Katmai 1912 (largest of the 20th century)

• The Katmai eruption set the minimum of global temperatures for the 20th century (and very likely beyond)

2. Period ~1912 to ~1942

• The long term solar cycles show a modulation such that successive solar maxima are roughly similar, and change slowly, over roughly century time scales

• Sunspot numbers are a fairly good proxy for solar activity, and recall that there is a 0.1% modulation in the solar luminosity with the solar cycle, and stronger solar cycles are associated with higher solar luminosity of similar scale

• During this period, solar sunspot maxima were trending higher, and the inferred solar luminosity (we have no direct measurements of solar luminosity back in those days) was rising

• Climate models show that in addition to rising anthropogenic CO2, solar activity likely accounted for a significant part of the temperature rise seen at this time, with deforestation and emergence from the Katmai eruption cooling also being significant.

• Also contributing, was a quiet period of no significant volcanic eruptions to inject cooling aerosols, compared to the 1883-1912 period.

• See next slide….

Climate modelling (e.g. Hansen 2005) shows increasing solar activity and accompanying luminosity rise likely accounts for a part of 1900-1945 global temperature rise. Forcing level is not shown on these graphs. Timing is what is being shown.

3. Period WWII to ~1970• Post WWII period of rapid rebuilding and rapid

industrialization• While CO2 levels are rising, what is rising faster is the

smoky, choking pollution of aerosols associated with coal burning, rapidly rising vehicle-miles, and power plants.

• Unburned hydrocarbons combine with sunlight, and water with sulfates to produce hydrosulfuric acid droplets and other particles which reflect incoming sunlight and cool the surface.

• The so-called “aerosol indirect effect” - These particles are also large enough to act as cloud nucleation sites and increase low clouds (this air pollution usually hangs low to the ground due to temperature inversions).

• (I grew up in L.A. in this period. You youngsters cannot believe how bad it was back then. You were lucky to be able to see 2 miles through the smog, and seeing the San Gabriel Mountains 20 miles away was a rarity.

• At the same time, World War II destroyed a lot of life and industrial capability, and it took some time for this to be rebuilt. There was a period of reduced growth in greenhouse gases at the beginning of this period.

• Also, the rising solar luminosity (as inferred from the sunspot cycle) came to a top in mid 1950’s and has been declining every since.

• The combination of lowered rate of GHG emission and much higher anthropogenic reflective pollutants, and a halt to solar-induced luminosity increases was enough to halt global warming and keep temperatures roughly constant during this 25 year period.

The Pennsylvania Smog Attack of 1948

London Smog 1952, killed 12,000 people

London – THE Smog Capital of that Time

But L.A. Provided Strong Competition

Los Angeles – Famous then as the of Smog Capitol of the United States

New York – Not Much Better

The Smog Machine!

Smog Particles –from R. Healy (looks like a couple of pollen grains at upper left as well)

4. ~1970-Today• Greenhouse gas emissions accelerate • The Clean Air Act of 1970 and other air

pollution laws in the U.S. and Europe cause a significant reduction in cooling aerosols, while China and Asia make up for these improvements with large post-Mao industrialization, largely coal-fired. Net global aerosol effect is approximately a wash, as can be seen in Hansen et.al. 2005.

• Solar and other effects are negligible compared to greenhouse gas emissions, primarily CO2 from oil, gas, gasoline, and coal burning

• Strong and accelerating greenhouse warming dominates climate forcings

14 sec video – Worldwide Temps 1976-2012

• https://www.youtube.com/watch?feature=player_embedded&v=ZAp1o-669xc

Heating and Cooling Forcings to the Earth’s Heat Budget (from Hansen et.al. 2005). Forcings calibrated from observations. Combined with the GISS Climate Model, they reproduce observed global temperature in detail very well. See next slide

(from Hansen et.al. 2005) Before 1900, the observed curve is based on observations at meteorological stations and the model is sampled at the same points, whereas after 1900 the observations include sea surface

temperatures for the ocean area, and the model is the true global mean (Hansen et. al. 2001).

Notes on Climate Forcings from Hansen et. al. 2005

*Effective forcings are derived from five-member ensembles of 120-year simulations for each individual forcing and for all forcings acting at once [see (9) and supporting online material]. The sum of individual forcings differs slightly from all forcings acting at once because of nonlinearities in combined forcings and unforced variability in climate simulations.

* This is the ozone forcing in our principal IPCC simulations; it decreases from 0.24 to 0.22 W/m2 when the stratospheric ozone change of Randel and Wu (S1) is used

* Ozone and black carbon forcings are less than they would be for conventional forcing definitions (11), because their ‘‘efficacy’’ is only 75% (9)

IPCC AR4 (2007) Climate Forcings: Human and Natural from 1750-present

2. Sea Level Changes

Thermal, melt water, salinity, geoid changes and relation to global temperatures

On the ~60 year time scale, sea level rises for two reasons, both are climate-related…

• 1. Thermal expansion of warmer water (simple physics. Observe temperature profile of the ocean, integrate, derive the thermal expansion)

• 2. Melting of continental “permanent” ice (glaciers, land ice caps)• While thermal expansion has provided most of the total of the past

100 years continental melt is rapidly increasing, and now contributing ~1/3 of the current sea level rise rate.

• Sea Level Rise rate = 1.8mm/year avg’d over past 100 years, but is 3.3mm/year avg’d over the past 20 years.

• Note that sea ice melting contributes nothing to sea level rise, since floating ice already displaces water (Archimedes Principle). Thus, melting of the Arctic Ocean ice happening now is not contributing to sea level rise

• On longer time scales, there is minor contributions from slow rebound of the land from the last Ice Age (loss of heavy glaciation causes continental land to float a bit higher, and this process is very slow).

• On time scales of a few years and shorter, there are many factors affecting sea level: tides, El Nino’s, tsunamis, changing atmospheric pressure associated with storms, floods and associated salinity changes…

• 34 second video of Greenland areas of ice melting (in red)

Sea Level Rise vs. Time and Place

• El Nino’s tend to cause sharper rises in sea level where the warm surface waters are, from the thermal expansion of water

• La Nina’s (the cold surface water phase) does the opposite

• The height of the geoid (the gravitational potential surface of the Earth; a surface parallel to sea level if all other factors are ignored) changes near Greenland and Antarctica especially, as glacial melt takes mass away from these continental masses

• Hence, the rate of sea level rise varies from place to place at different times. Must take account of geoid changes (straight-forward gravity) and other data sampled widely in location and time to get it right.

• The following data shows the many tidal gauges and satellite measurements are doing a good job of tracking global sealevel rise

How does this rise rate compare with Ice Age transitions? Red line is 1.8mm/yr = 20th century average. Recent rate is higher: 1993-2003 satellite observed rate is 3.3mm/yr

GRACE Satellite uses gravity to measure total ice mass loss from Greenland. Ice loss is accelerating.

Estimates of total Antarctic land ice changes and approximate sea level contributions using many different measurement techniques. Adapted from The Copenhagen Diagnosis. (CH= Chen et al. 2006, WH= Wingham et al. 2006, R= Rignot et al. 2008b, CZ= Cazenave et al. 2009 and V=Velicogna

2009) (Source here)

Ice mass changes for the Antarctic ice sheet from April 2002 to February 2009. Unfiltered data are blue crosses. Data filtered for the seasonal dependence are red crosses. The best-fitting quadratic trend is shown as the green line (Velicogna 2009).

Monthly changes in Antarctic ice mass, in gigatons, as measured by NASA’s GRACE satellites from 2003 to

2011. Results from five different IMBIE team members using different methods. The data have been adjusted to

reflect new models of post-glacial rebound.(Shepherd et.al. 2012).

What about glaciers globally? Maybe it’s just Greenland and

Antarctic glaciers that are melting?

No.

Global Melt of Glaciers, in equivalent water thickness (black boxes, m/yr), and cumulative total thickness loss (red boxes, right

scale, meters). Glacier melt is clearly accelerating rapidly

Annual change in global glacier melting to sea level rise (left axis, mm of water equivalent, mm/yr) and cumulative value (right axis, mm), based on surface area-

weighted mass balance observations. (source)

The speed of melting (meters of glacier depth per year) of 23 different Antarctic glaciers vs. the temperature of the seawater into which they

contact, where 0 is the freezing point of (salt) water. Clearly the rate of melting rises rapidly with even small temperature differences above the freezing point. Data from satellites and ground surveys (Rignot & Jones

2002)

Arctic Ocean Ice Cover – Dropping More Rapidly than the 2007 IPCC AR4 models

Arctic ice coverage is dropping in all seasons, not just summer

Not just ice coverage area, but ice volume is dropping even more dramatically, as the

permanent ice rapidly disappears, leaving only thin seasonal ice

Summer Sea Ice Area; past 1,450 years. In 2012, a new record low of 3.5x10^6 km^2. That is less than half the value of the

bottom point of this curve. See the Latest data

Let’s Put Recent Global Warming in Context of the Last ~1000 Years

From Mann et.al. 1999. The “Hockey Stick” made famous in “An Inconvenient Truth”

Temperature Proxies for Century, Millenium Time Scales• (See Mann et.al. 2008 and here, for more details), but briefly…• Foraminifora: growth sensitive to temperature; different for different

species. Preserved in sediments• Tree rings; show good correlation to other proxies, until the 20th

century (likely because CO2 levels also affect tree rings and CO2 levels now far above typical values of past 1000 years

• Stalagmites: annual growth ring thickness (water from above) sensitive to temperature and climate in general

• Ice cores: trapped air bubbles preserve atmosphere, and isotope ratios are sensitive to temperature. Also trap pollen, species sensitive to temperature

• Pollen species composition in sediments from lakes, layering showing annual runoff, charcoal shows major fires which can be cross correlated with other data

• Borehole temperatures: surface temperatures conduct downward through the ground, and deep measurements contain information on ancient temperatures. See NOAA’s site on borehole science

Given the importance, the work was re-done with a wider range of temperature proxy assumptions and additional care to avoid

statistical over-fitting. Still a Hockey stick. Note the Medieval Warm period is actually a Northern Hemisphere phenomenon, not

global.

Glacier length change from temperature proxies: Old photos, and written accounts. Still a hockey stick

Global surface temperature change over the last five centuries from boreholes (thick red line). Shading represents uncertainty. Blue line is a five year running average of HadCRUT global surface air temperature (Huang 2000). Borehole

data confirms the other temperature proxies.

Jones and Mann (2004) temperature reconstructions using proxies, now going back almost 2000 years, with global temperatures at the bottom pane. Actual instrumental temperatures shown in red. Proxies and instruments both agree

- still a Hockey Stick

Other Climate Change Effects

• Global phytoplankton has declined by an alarming 40% since 1950, as warmer, more stratified ocean surface waters inhibit nutrient mixing from below and thus limit growth

• The stratosphere is cooling, as rising stratospheric CO2 gets less IR from below but radiates more IR because of collisional excitation followed by radiative de-excitation. We showed this earlier in the course.

Night Temperatures Rising Faster than Day Temperatures…• …causes a decrease in the daily temperature range, which has

been observed (Braganza 2004). • This too is a unique prediction of Greenhouse Effect warming

(Alexander 2006). Why? Because temperatures reflect the integrated heating that has already happened during the day, so that peak temperatures occur in the late afternoon, not at noon as you'd naively expect if there were no lag. The hot ground can't efficiently radiate away this heat because it is trapped by CO2, and this keeps night-time temperatures warmer.

• Daytime temperatures are warmer too, but not as much at night time temps because it is not increased incoming sunlight that is causing Global Warming, it is human-caused greenhouse gases inhibiting re-radiated cooling, which happens mostly late evening, AFTER the incoming solar heating.

• A particularly dramatic demonstration of this can be seen in the mid/late 20th century data, when cooling by human-generated aerosol pollution caused daytime temperatures to stay roughly constant in spite of increasing CO2, while nighttime temperature actually increased (Wild, Ohmura, and Makowski 2007).

Night-time minimum temps are rising faster than are daytime maximum temps, although both are rising. This is a unique signature of

GHG-caused warming

Why is This Happening to Us!?

• Why?... Us! We human beings - we’re doing it! We’ve raised CO2 levels from ~280ppm to 400ppm in just the last 130 years, and it’s accelerating rapidly.

• How? By sheer number and dominance. As recently as 1900, wild mammals made up ~50% of the land biomass. Now, only 3%. Humans and their livestock make up 97% of the vertebrate biomass on land (Bodley 2008), and 72% of ALL vertebrate biomass on land or sea. (90% of the large fish have already been fished out, so that makes our domination that much easier).

• 36% of the primary productivity of the entire planet has been diverted to humans (Haberl, et.al. 2012)

This 2008 graph is already out of date. Population passed 7 Billion in 2012. Human population is rising now at an amazing and

unsustainable rate of 1 billion additional people every 13 years.

• We’re forcing CO2 into the atmosphere at a rapid rate, taking the cumulative carbon sequestration of hundreds of millions of years (the Carboniferous Era) and burning it all at once – in a geologic instant.

CO2 Levels from ice cores, for the past ~1 million

years

Progressively expanded time scale needed to show how incredibly rapid is the CO2 rise of

today vs. geologic past

CO2 Levels - past 60 years

But maybe the CO2 is not from us, but instead from volcanoes or

something else?

• No. The CO2 is ours.

• Volcanoes put out only 1% of the CO2 that humans inject annually into the atmosphere

• How do we know that CO2 is ours? There are many independent confirmations it’s ours, which I’ll number as follows….

1. We’re injecting far more than enough CO2 into the atmosphere to account for the observed rise (some goes into

the ocean, some into plants and soil)

Global Temperatures vs Atmospheric CO2 vs CO2 Emissions by Humans – Last 1000 Years.

2. Note how the growth rate of CO2 drops during economic recessions. 10 year averages are the unmarked bars. I’ve added economic recessions (Fed

data) labeled with years. The “oil shock” recessions of ’74 (Arab oil embargo) and the ’91 (Gulf War) are particularly obvious

3. Plants (hence, fossil fuels) preferrentially take up carbon-12 (C12). As fossil fuel generated CO2 rises since the dawn of the industrial age, C13 is expected to make up a declining fraction of total atmospheric carbon. From known emission levels, we can predict the ratios, and the observations shown above are just what models predict. Note too the much more rapid drop in C-13 after 1950 (see at right), with post-WWII rebuilding. The conclusion is inescapable - the rapidly rising CO2 we see is human-caused, mainly by fossil fuel burning. (From Francey etal 1999)

Methane: Coming from domesticated cattle, and from melting permafrost and peat, is 25x more powerful as a

greenhouse gas than CO2, per kg (avg’ed over 100 yrs)

• Melting Permafrost Accelerating Global Warming – methane trapped in melting Arctic Lakes is being released

• K. Anthony (U. Fairbanks) on Arctic lake methane

• Note, CH4 oxidizes to H2O + CO2. The residence time of a CH4 molecule in the atmosphere is about 10 years. Both H2O and CO2 are less powerful greenhouse gases than methane.

Fraction of total emission of carbon which (top frame) remains in the atmosphere, (middle) taken up by land biosphere, and (bottom) taken up by ocean. Time period is

1960 – 2007. Note as the ocean absorbs more CO2 and also warms, it is becoming less effective at soaking up additional CO2. The opposite is true on land (sorry for the

terrible repro of this tiny graph)

Deforestation: Human Fingerprint Since Dawn of Civilization

• Tropical deforestation, as countries scramble to sell off their timber and clear cut so they can grow cattle (and soybeans, sugar), accounts for nearly 20% of carbon emissions (Canadell et.al. 2007)

• In Indonesia’s main island of Sumatra, home of the last Sumatran Rhinos, deforestation destroys 5 football fields worth of rainforest per minute.

• Forests remove ~2.4 billion tons of carbon from atmosphere per year (Canadell et.al. 2011)

• Regrowth from cessation of tropical forest clearing shows rapid carbon uptake into trees, and also into root systems underground

• But Slash / burn adds significant carbon to atmosphere, as has been done for thousands of years, and still goes on in the Amazon and other places.

Deforestation: Produces about 1/3 as much CO2 per year as fossil fuel

burning

Causes of Amazon deforestation: Cattle Ranches, Mostly. Demand from rapid

proliferation of fast food outlets world wide

Deforested Land Shown in Red – NASA image

Effects of Deforested Land on Climate

• 1. Carbon burned or otherwise put back into the atmosphere as CO2

• 2. Loss of photosynthesis = loss of ability to pull CO2 out of atmosphere

• 3. Desertification of land – this may actually cause some cooling (although I can’t find data), via higher reflectivity of land vs. forest

• 4. Healthy forest returns ¾ of rainfall back to the atmosphere where it can rain out elsewhere. Deforested land returns only ¼ of rain water back to the atmosphere for further downwind rainmaking, instead causing severe runoff, erosion, loss of topsoil, and loss to the ocean

Key Points – Current Climate Change and Global Warming (GW)

• Solar luminosity, cosmic ray modulation, show no secular change since ~1950’s – cannot be causing GW

• 20-21st Century climate: 3 regimes and their causes• Volcanic and human pollution aerosols: net coolant to climate by reflecting

sunlight. Volcanic CO2 production only 1% of human-generated CO2.• Climate models (w/ high, low clouds, aerosols, volcanics, GHG’s,

deforestation, solar) agree closely with observed global temps.• Atmospheric CO2 is human-caused, as shown by C13/C12 ratio changes.• Fossil fuel burning dominates climate forcing• Sea level rises due to thermal expansion of warmer seawater, and (rapidly

increasingly) melting land ice• Deforestation removes carbon sequestering trees, altering carbon cycle

equation.• Methane as greenhouse gas forces climate at ~1/4 that of CO2. Methane

levels have tripled from human activities, since the pre-industrial times.• Night-time low temps are rising faster than are day-time maximum

temperatures. • Tropical deforestation goes mostly to cattle ranches to satisfy fast-food

restaurant demand