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By Daniel A. Gross

Most economists agree that if we want to efficiently reduce CO₂ emissions, we’ll need to put a price on carbon. But a nagging question remains. How are we supposed to figure out a price for an invisible, amorphous gas that underpins the economy and transforms the climate?

It’s relatively easy to put a price on a t-shirt or a pound of apples. Calculate the cost of all the inputs, from raw materials to labor to shipping. Then add a margin for profit, and the product is ready to be sold.

Why do the costs of carbon vary from country to country?

The costs of carbon, by contrast, are diffuse and diverse—which helps explain why the estimated prices of CO₂ vary wildly across countries and companies. The US government uses an estimate of $33 per ton of CO₂, while Sweden uses the strikingly high figure of $168. In internal calculations, Google Inc. uses $14 per ton, while (perhaps surprisingly) oil companies like BP and Exxon-Mobil use fairly high prices of $40 and $60, respectively.

So where do these carbon price tags come from? Whenever you see dollar amounts tacked on to tons of carbon, economists likely used one of two methods to calculate them.

Calculation methods vary too

The first method is like a very long addition problem. The strategy, according to World Bank senior economist Stephane Hallegate, “is to look at the damages on the environment and societies and people that one ton of carbon would create.” In other words, economists use computer models to tally up all the negative impacts of carbon, and set a carbon price high enough to offset those costs. “If the damages are going to be high, that justifies quite a high carbon price,” explains Niven Winchester, an MIT environmental economist.

In practice, however, adding up the costs of carbon can be extremely tedious. “You’re solving a puzzle,” he says—but the puzzle has a huge number of finicky pieces. A dizzying array of factors can affect the estimated cost of carbon. For example: How much will solar energy cost in 30 years? How much meat will humans consume, one century from now? How much CO₂ would cause the Greenland ice sheet to melt? Because there are so many factors to estimate, MIT outsources its calculations to a massive computing center 100 miles west of Boston, the Massachusetts Green High Performance Computing Center (MGHPCC). Unlike simplified models of the economy, “integrated models” may generate datasets of many terabytes — a reflection of the many environmental and economic processes that researchers hope to capture.

Read the full article at roadtoparis.info

Report highlights enormous potential and discusses pathways toward affordable solar energy.

By David L. Chandler | MIT News Office

According to present plans, the Grand Ethiopian Renaissance Dam (GERD) — now under construction across the Blue Nile River in Ethiopia — will be the largest hydroelectric dam in Africa, and one of the 12 largest in the world. But controversy has surrounded the project ever since it was announced in 2011 — especially concerning its possible effects on Sudan and Egypt, downstream nations that rely heavily on the waters of the Nile for agriculture, industry, and drinking water.

To help address the ongoing dispute, MIT’s Abdul Latif Jameel World Water and Food Security Laboratory (J-WAFS) convened a small, invitation-only workshop of international experts last November to discuss the technical issues involved in the construction and operation of the dam, in hopes of providing an independent, impartial evaluation to aid in decision-making. The group’s final report, which was shared with the three concerned governments in early February, is being released publicly today.

On March 23, the three governments signed an agreement to enter negotiations for final settlement of issues surrounding the dam’s operations. Though the agreement is preliminary, it marks a significant step forward.

Professor John H. Lienhard V, the director of J-WAFS, was among the organizers of the November workshop held at MIT. He says that the group was carefully selected to include top experts on water resources engineering and economics and on the Nile Basin, and was charged with reviewing the current state of technical knowledge on the GERD and its potential downstream impacts. The idea was “to give advice, and do it impartially,” Lienhard says.

“We went out of our way to find people who know about large dams and large rivers, and who are not affiliated with any of the three governments,” including people with “hands-on experience with dams of this scale,” Lienhard says. The meeting also included observers from Egypt, Sudan, and Ethiopia. After the report was shared, members of the group also met with officials in Egypt and Ethiopia to review the technical issues.

Technical issues

The working group developed consensus recommendations, which were incorporated into the 17-page report. It reflects agreement reached at the November workshop, says Lienhard, who is also the Abdul Latif Jameel Professor of Water and Food at MIT.

The report raises five technical issues that require resolution. First, the GERD will join the Aswan High Dam as a second large reservoir on the Nile River. Egypt and Ethiopia need to formulate a plan for coordinating the operation of these two dams, so as to equitably share Nile waters during periods of reservoir-filling and prolonged drought. Nowhere in the world are two such large dams on the same river operated without close coordination.

Second, the design of the GERD requires that a very large “saddle dam” be built to prevent water stored behind the GERD from spilling out of the northwestern end of the reservoir. The risks associated with a possible failure of this saddle dam may not have been fully appreciated, and must be carefully managed.

Third, there is concern about the location and capacity of the GERD’s low-level release outlets to provide water to Egypt and Sudan during the reservoir’s filling or periods of drought.

Fourth, the hydropower generated from the GERD exceeds Ethiopia’s current domestic power market, and it will therefore need to be sold outside Ethiopia. A plan is needed for such sales, and for the construction of transmission lines to regional markets. A power trade agreement will ensure that the Ethiopian people receive a good financial return on their investment.

Fifth, the ongoing accumulation of salts in the agricultural lands of the Nile Delta could accelerate rapidly; additionally, the GERD will enable Sudan to increase irrigation withdrawals upstream, further reducing the water available to Egypt. Studies are urgently needed to identify the magnitude of these potential problems, and to mitigate their impact.

Managing the flow

Perhaps the biggest question concerning the new dam is how Ethiopia will manage the process of filling its huge reservoir, whose capacity equals more than a year’s flow of the Blue Nile. Egypt has expressed concerns that if the reservoir is filled too quickly, it could severely diminish the flow upon which Egypt depends; 60 percent of the nation’s water comes from the Blue Nile.

“The Egyptians are very concerned about what a reduction in the amount of water would mean to them,” says Kenneth Strzepek, a research scientist at MIT’s Joint Program on the Science and Policy of Global Change, and a co-chairman of the November workshop.

Dale Whittington, a professor at the University of North Carolina and a co-editor of the MIT report, says: “Egypt, Ethiopia, and Sudan are currently hoping that a team of international consultants can quickly find technical solutions to these challenging problems to which they can agree. From our perspective, this is likely wishful thinking. The hard negotiations ahead will require that foreign policy and water experts from each of the three countries have a shared understanding of the technical issues and a willingness to compromise while hammering out detailed agreements on reservoir operation policy, power trade agreements, dam safety, and salinization control.”

But, Whittington says, “A shared knowledge base and modeling framework is unfortunately lacking, despite over $100 million in investment by the Nile Basin Initiative over more than a decade of engagement.”

Don Blackmore, former executive director of the Murray-Darling River Basin Authority in Australia and current chair of the International Water Management Institute, says, “Egypt, Sudan, and Ethiopia will try to work with their consultants to solve these five problems, but if these countries request assistance, we believe that the international community has an obligation to step forward.”

Other nations can potentially play three roles, says Blackmore, who was not involved in compiling the new report: providing impartial scientific advice; bringing legal expertise and experience on transboundary waters to help craft the text of technical agreements; and serving to arbitrate disputes that arise over time.

Given the potential for conflict among the nations dependent upon this water, Blackmore adds, “The international community needs to focus on the Nile as a matter of urgency.”

By Cassie Martin | Oceans at MIT

Earlier this year, weather and climate agencies around the world declared 2014 the warmest year on record, even though the increase in global mean temperature has slowed. This warming “hiatus” has puzzled climate scientists, as it deviates from climate models which project a continuing temperature increase. Climate expert Jochem Marotzke visited MIT last week to deliver the 15^th annual Henry W. Kendall Memorial Lecture “Recent Global Temperature Trends: What do they tell us about anthropogenic climate change?” in which he discussed the hiatus as well as the abilities and limitations of climate models.

Marotzke is a director at the Max Planck Institute for Meteorology in Hamburg, Germany, and was an MIT EAPS faculty member in the 1990s. He has spent his career researching the role of the ocean in climate and climate change, and recently expanded his interests to include multi-year to decadal climate prediction. “If you look at other central indicators of global climate, such as sea ice melt, ocean heat uptake, and sea-level rise, they show that global warming is continuing,” Marotzke said. “But this particular indicator, global surface temperature, is rising at a much lower rate now. This is something that as a climate research community we need to take seriously; we need to understand it and communicate the issues about it.”

For the past 15 years, increases in global mean surface temperature has slowed contrary to what climate model simulations predicted. Known as the warming “hiatus”, this phenomenon is largely due to natural variability: Cyclical climate processes such as La Niña and fluctuations in the amount of solar radiation reaching Earth’s surface can disrupt the warming trend. Additionally, the oceans absorb an enormous amount of excess heat energy trapped by the atmosphere—as much as 93 percent, Marotzke said. Light-reflecting aerosols from volcanoes also contribute to the slow down.

The failure of climate models to predict this hiatus has long perplexed scientists and bred some public mistrust in climate models. Climate change skeptics claim the hiatus is proof that global warming doesn’t exist, and that climate models overestimate greenhouse gases’ warming effects. Marotzke ardently disagrees. He shared with the audience a study published in Nature earlier this year in which he and co-author Piers Forster of the University of Leeds analyzed 114 model simulations of 15-year global mean temperature trends since the beginning of the 20^th Century. If their analysis showed that models consistently overestimated or underestimated the amount of warming compared to real-world observations, then the models must have a systematic bias.

Fortunately the simulations performed fairly well, producing a range of predictions for each 15-year period in which actual observed temperature trends for those periods fell. Even if the observed trends at times fell close to range edges, they were not biased to one side or the other. Although the models didn’t accurately predict the current warming hiatus, which is not unusual, they also failed to predict other accelerated warming or hiatus events. In fact, the models underestimated warming in some periods compared to the observations. “The claim that models systematically overestimate warming from increasing greenhouse gas concentrations is unfounded,” said Marotzke.

To find out what these simulated short-term temperature trends actually tell us about the climate, Marotzke and Forster performed a multiple regression analysis, which aimed to identify the most significant factors contributing to the trend. For shorter 15-year periods, the analysis found random natural variability in the climate system had the largest influence—approximately three times the impact of all other physical factors combined. Only when Marotzke and Forster analyzed model simulations of global mean temperature trends spanning 62 years did differences in factors including ocean heat absorption, greenhouse gas concentration, and aerosol pollution begin to make a noticeable difference.

In other words, modeling 15-year-long periods only shows the impact of natural variations in the climate system. To see anthropogenic influences on climate change, we have to look at the bigger picture. “The hiatus masks anthropogenic warming,” said Marotzke. “It is a huge distraction, but an incredibly fascinating one.”

The 15th Annual Henry W. Kendall Memorial Lecture was sponsored by the MIT Department of Earth, Atmospheric and Planetary Sciences and the MIT Center for Global Change Science. The lecture series honors the memory of Professor Henry Kendall (1926-1999), a 1990 Nobel Laureate, a longtime member of MIT’s physics faculty, and an ardent environmentalist. A founding member and chair of the Union of Concerned Scientists, he played a leading role in organizing scientific community statements on global problems, including the World Scientists’ Warning to Humanity in 1992 and the Call for Action at the Kyoto Climate Summit in 1997.

Watch the full lecture here.