Energy on this world and elsewhere Instructor: Gordon D. Cates Office: Physics 106a, Phone: (434) 924-4792 email: cates@virginia.edu Course web site available at www.phys.virginia.edu, click on classes and find Physics 1110. or at http://people.virginia.edu/~gdc4k/phys111/fall17/home.html Lecture #15 October 12, 2017
Announcements Read Preface and Chapters 1-2 of Smoke and Mirrors Read Chapters 3-5 of Smoke and Mirrors Read Chapters 6-9 of Smoke and Mirrors Read Chapters 5 and 6 of class notes. Tentative date for next quiz: Thursday October 19 th. Visiting today: Prof. Paschke
Greenhouse gases and the greenhouse effect
Is the greenhouse effect real? Yes! - we wouldn t be here without it! Venus has a runaway greenhouse effect. - Venus receives roughly twice the sunlight of the earth. - In the absence of the greenhouse effect, its average temperature would be 90 o F. - With the runaway greenhouse effect, its average temperature is 800 o F. Mars has only a very small greenhouse effect. - In the absence of the greenhouse effect, its average temperature would be -65 o F. In fact, there are huge variations ranging from roughly -225 o F to as high as 70 o F Earth s greenhouse effect is just right (for us). - In the absence of the greenhouse effect, Earth s average temperature would be -4 o F. - With the greenhouse effect, the Earth s average temperature is roughly 60 o F.
Greenhouse gases over 2000 years With greenhouse gases, the anthropogenic origin is unambiguous.
CO 2 concentration over ten thousand years From the 2008 National Academies report. Whatever you end up concluding about global warming, there is no question that we have increased the carbon dioxide levels in our atmosphere by something like 40% (around 35% shown) since the beginning of the industrial revolution.
Accelerated warming of the Earth Figure from: Shaopeng Huang, Henry N. Pollack and Po-Yu Shen, Temperature trends over the past five centuries reconstructed from borehole temperatures, Nature 403, 756 (2000). Global 0.0-0.5 Taken at face value, this paper clearly shows accelerated warming associated with the post-industrialization world - just one example that CO 2 and other anthropomorphic greenhouse gases are dominating global warming trends. Temperature relative to present day (K) 0.0-0.5-1.0 Northern Hemisphere Southern Hemisphere 1500 1600 1700 1800 1900 2000 Year -1.0 0.0-0.5-1.0
Temperature and CO 2 concentration over several hundred thousand years From the 2008 National Academies report. It is probably the case that warming on the Earth, with no other factors, causes CO 2 to levels to rise. Even if this is true, the recent rise in CO 2 is virtually impossible to explain other than anthropogenic causes, and unprecedented in 500,000 years.
How does the greenhouse effect work?
Blackbody or thermal radiation Heat or thermal radiation is emitted at longer, so-called infra-red wavelengths. The camera being used is only sensitive to the long wavelengths associated with thermal radiation. Stefan-Boltzmann equation: P radiated = σ ε AT 4 Here σ = 5.67 x 10-8 W/(m 2 K 4 ), ε is called the emissivity and is between 0 and 1, A is the area of the thing radiating, and T is its temperature. Wien s displacement law λ max = b/t Here lambda is the central wavelength of the radiation emitted, b = 2.9 x 10-3 m K, and T is the emitting objects temperature.
Blackbody or thermal radiation The camera being used is only sensitive to the long wavelengths associated with thermal radiation. Stefan-Boltzmann equation: P radiated = σ ε AT 4 Here σ = 5.67 x 10-8 W/(m 2 K 4 ), ε is called the emissivity and is between 0 and 1, A is the area of the thing radiating, and T is its temperature. Wien s displacement law λ max = b/t Here lambda is the central wavelength of the radiation emitted, b = 2.9 x 10-3 m K, and T is the emitting objects temperature.
What is the temperature of a planet in the absence of the greenhouse effect? Radiation from the sun deposits energy on the earth Earth Thermal radiation from the earth keeps temperature in equilibrium The Earth absorbs light from the sun, some quantity, P absorbed Thermal radiation is emitted by the Earth: P radiated = σ ε AT 4 The two must EXACTLY balance one another for the Earth s temperature to be in equilibrium: P absorbed = P radiated For the Earth, I find T= 250.7 K or -8o F.
The greenhouse effect - a simplified model Visible light is absorbed by the earth. The earth re-radiates the energy in the form of infrared radiation. The infrared is largely absorbed by water vapor and CO 2 and reradiated, both into space, and back to the earth. I find that T new=2 1/4 T no greenhouse = 298.1K or 76.9 o F (correct answer is 60 o F)
Realistic Climate Models While the simplistic model from the previous slide provides a decent quick estimate of the effect of the greenhouse effect, a more serious treatment must contain many subtle effects. Among the many things missing from the simplistic model are: Positive feedback loops: for example, CO 2 causes warming, warming causes more moisture due to evaporation, water vapor causes still more warming. Negative feedback loops: for example, more water vapor causes more clouds, clouds are good at reflecting sunlight back into space, less absorbed light causes cooling. Other factors: aerosols, particles in the air, can cause cooling or warming. Local effects: taking into account all the complex local dynamics. And much much more.
The IPCC Reports The Intergovernmental Panel on Climate Change (IPCC) was formed under the auspices of the United Nations to provide the world with a better understanding of human caused climate change. The last two reports were released in 2007 and 2014 and are referred to as AR4 and AR5 respectively. The IPCC reports are probably the best place to get a sense of the consensus view of climate change.
The IPCC Reports AR4 AR5 The basic messages of the AR4 and AR5 reports were quite similar. Because warming was milder than expected over the time frame of 1998-2012, however, the predictions for warming in AR5 were modestly lower than in AR4.
The difference between predictions from the 2007 (AR4) and 2014 (AR5) IPCC Reports From page 44 of the IPCC AR5 report
The 1998-2012 warming plateau (such as it is) Yu Kosaka and Shang Pie Xie, Nature vol. 501, pg. 403 (2013) While the 1998-2012 plateau is nothing to write home about, it is nonetheless the case that most climate models (111 out of 114) failed to predict it.
Just the red and black lines: slope? or no slope?
Just the red and black lines: slope? or no slope?
Just the red and black lines: slope? or no slope?
Just the red and black lines: slope? or no slope?
Just the red and black lines: slope? or no slope? This is 3 years, plus the plateau. plateau appeared in a lot of literature, but it is a terrible name. IMHO: over-reading the data. But it was an unexpected warming slowdown. There also were many bad-faith claims in the press about how warming had stopped. This was never justified.
The 1998-2012 warming plateau (such as it is) Yu Kosaka and Shang Pie Xie, Nature vol. 501, pg. 403 (2013) While the 1998-2012 plateau is nothing to write home about, it is nonetheless the case that most climate models (111 out of 114) failed to predict it.
Long term climate trends lie underneath variations with varying time scales: yearly, few years,decadal Example: Pacific Decadal Oscillation
Realistic Climate Models from IPCC reports AR4 AR5
What is the takeaway message of the two IPCC reports? The central value of the expected warming due to a doubling of CO 2 over preindustrial levels has dropped from roughly 4 o C to around 2.5-3.0 o C. The range of expected temperatures (due to uncertainties) appears to me to have dropped somewhat from around +/- 1.75 o C to around +/- 1.25 o C (a quote from Nature I will show shortly suggests a somewhat wider, basically unchanged, range more like the earlier +/- 1.75 o C. A quadrupling of CO 2 over pre-industrial levels might cause warming of 3 o C - 6 o C, which is potentially disastrous.
Comments in Nature on the new IPCC report
Possible non-natural causes of over estimates of warming First, it should be said that climate models are complex, and there are many opportunities for errors. One example: William Happer argues that the absorption of infrared by CO 2 is being overestimated. He bases his argument on a dearth of knowledge about the absorption of light in the far wings of the CO 2 absorption lines (more on this in a moment). Surprisingly, research to better understand absorption in the far wings is not currently taking place.
The first person to describe the Greenhouse effect quantitatively: Svante August Arrhenius Arrhenius proposed the equation below in 1896: T = ln(c/c 0 ) The equation suggests that the change in temperature, when CO 2 concentrations change from C 0 to C, will be proportional to the natural logarithm of the ratio C/C 0. Arrhenius equation is still valid and used to this day. The logarithmic dependence on C/C 0 implies that any additional absorption is taking place well away from the line centers of CO 2 absorption lines. That being the case, it is clearly important to understand the far wings of the CO 2 absorption lines.
Is global warming from greenhouse gases what we should be most worried about?
Important questions Is the Earth getting warmer? Is the rise in CO 2 levels in the atmosphere due to human activity? To what extent is the anthropogenic CO 2 the cause of the warming? What are other effects of the CO 2?
The acidification of the oceans As the PH of the oceans decrease, things with carbonate-based shells or exoskeletons are at risk of leeching out carbonates. This is believed to be happening already, and is a major contributing factor to the massive die offs of coral reefs around the world. Annual Reviews of Marine Science, Volume 1, pg. 169 (2009); 1362 citations!!!
Past mass extinctions
Past mass extinctions
The potential for new mass extinctions
Gordon s view of the world The Earth is getting warmer. We are flooding the atmosphere with CO 2. It is nearly certain that CO 2 is causing much of the warming. - If you press me, I tend to favor the lower end of the IPCC predictions. - I base this view, in part, on Happer s arguments about CO 2 absorption. I am extremely concerned about the other effects of CO 2, such as the acidification of the ocean. More generally, it appears as if the oceans, as we know them, are dying. This, not the degree of warming due to CO 2, should be our focus. An analysis of this statement goes beyond this course. The environmental effects of our energy-hungry civilization and our population of 7+ billion need to be mitigated immediately.
Renewable Energy Sources
Renewable Energy Sources Hydroelectric Biomass Biofuels Wind Waste Geothermal Solar thermal Solar photovoltaic Tidal
Putting renewable energy sources into perspective TPES = Total [world] Primary Energy Supply From this table, we can see that photosynthesis does not have a great edge when it comes to providing a big chunk of TPES
Renewable Energy Sources Much lower energy density than fossil fuels. Low energy density can make the economical implementation of technology challenging. Sometimes history can be a great teacher regarding what is truly practical. - - Windmills have been around for at least a thousand years. Ethanol has been used as a fuel, EVEN FOR INTERNAL COMBUSTION ENGINES, since early in the 19 th century.
Renewable Energy: fraction of primary energy consumption in 2008 Solar/PV 1% Geothermal 5% Waste 1 6% Wind 7% Nuclear Electric Power Biofuels² 19% ` 9% Coal 23% Petroleum 37% 7% 7% Renewable Energy Wood 28% Natural Gas 24% Hydroelectric Power³ 34%
Renewable Energy: fraction of primary energy consumption in 2011 Solar/PV 2% Geothermal 2% Waste¹ 5% Wind 13% Nuclear Electric Power ` 8% Coal 20% Biofuels² 21% Natural Gas 26% 9% Renewable Energy Petroleum Petroleum 36% 37% Wood 22% Hydroelectric Power³ 35% 1 Municipal solid waste from biogenic sources, landfill gas, sludge waste, agricultural byproducts, and other biomass. 2 Fuel ethanol (minus denaturant) and biodiesel consumption, plus losses and co-products from the production of fuel ethanol and biodiesel.
Renewable Energy: fraction of primary energy consumption in 2014
How electricity is produced ~10 TWh / yr Note the large difference in the breakdown depending on whether one considers the Nameplate Capacity or the Net Generation
The changing face of electricity production Renewable are responsible for more than half the new generating capacity, but significantly less of the new net generation.
Rapid growth of wind and solar Wind Solar Meteoric rise will clearly make wind and solar even more important in the coming years.