Ambitious 2050 emissions targets cannot be achieved by conservation, refurbishment, and good design alone. Increased use of clean renewable energy will be required to close the gap. The onus is on the building industry to ante up the required intellectual effort and investment.

Scientific measurements have shown beyond doubt that the Earth is getting gradually warmer and that the level of carbon dioxide (CO2) in the atmosphere is on the increase. While some people may continue to doubt the link between these two phenomena or that the escalation in atmospheric CO2 is due mainly to human activity, it is now widely accepted in both scientific and political circles that man-made climate change is a reality.

The magnitude of change and the potential consequences are still open to debate, but there is general consensus that we should be focusing our attention on mitigation. Since the articulation of the Kyoto Protocol in Japan in 1997 and its global acceptance in 2005, 183 countries, including the entire European Community, have formally committed to significant reductions in CO2 emissions. Despite this, little real progress has been made, with the United States failing to sign the treaty and China and India (among many others) currently refusing to ratify it. Even among signatories, emissions have, in most cases, continued unabated. In fact, according to the United Nations Framework Convention on Climate Change, the Russian Federation, New Zealand, Italy, and others have actually increased their emissions significantly in the decade since signing the Protocol.

With the formation of the C40 Cities Climate Leadership Group in 2005, a large number of cities around the world have developed their own emission reduction targets. This is a fairly recent development, and it is too early to know if this initiative is achieving real results. However, in spite of all these good intentions, there is little or no clear guidance as to how one would go about achieving these ambitious targets.

What is clear is that the building industry has a pivotal role to play in achieving these reductions. A report on energy efficient trends in residential and commercial buildings published by the U.S. Department of Energy in 2008 states that buildings in the United States represented about 9 percent of worldwide carbon dioxide emissions in 2005 — or 2,318 million metric tons of carbon dioxide.

Historically, greenhouse gas emissions from buildings have been growing at a greater rate than those from other sectors. The same U.S. Department of Energy report states that the growth in buildings’ energy consumption has resulted in carbon dioxide emissions rising from about a third of total U.S. emissions in 1980 to almost 40 percent in 2005. This is primarily a function of the increase in electricity use in buildings, 70 percent of which is dependent on fossil fuels for its generation.

Nobody knows the degree to which these emissions need to be reduced to avert disaster. In the absence of scientifically based national targets, let us consider the implications of adopting the targets established by the Seattle Climate Protection Initiative. The goal of this initiative is to reduce Seattle’s greenhouse gas emissions by:

•    7 percent below 1990 levels by 2012
•    30 percent below 1990 levels by 2024
•    80 percent below 1990 levels by 2050

Figure 3 shows a notional pattern of reduction in CO2 emissions from commercial and residential buildings if the targets established by Seattle are to be applied across the nation.

Meanwhile, the U.S. population is expected to grow from its current level of 306 million to 438 million by 2050. This will undoubtedly be accompanied by a roughly proportionate increase in the building stock of 40 percent. Of the existing building stock, I estimate that 70 percent of current buildings will still be in use in 2050. The remaining 30 percent would have been demolished and rebuilt. Therefore, taking account of demolition, rebuilding, and overall growth, about half of the building stock in 2050 will consist of buildings that exist today, and the other half will be made up of buildings that have not yet been built.

If these buildings, still in use in 2050, are not upgraded in terms of their energy emissions performance, their emissions alone would be nearly five times the target emissions in 2050! This is indicative of the enormous challenge ahead.

Even if every new building built from now on is carbon neutral (contributing no net increase in atmospheric carbon), we will still be well short of the target unless we very significantly upgrade the existing building stock.

A report from the United Nations Environment Programme states that “There is a global potential to reduce approximately 29 percent of the projected baseline emissions from residential and commercial buildings by 2020 and 31 percent from the projected baseline by 2030.” This trend suggests that we could potentially reduce the energy consumption of existing buildings still in use in 2050 by half relative to today’s consumption. To go beyond that would likely involve accelerated levels of demolition and rebuilding.

With regard to new buildings, it is unlikely that many will be carbon neutral in the immediate future. There is no jurisdiction that demands this, and without a legislative mandate, only the most altruistic institutions will attempt to achieve this goal. Developers are unlikely to change their historic minimum-code-compliant approach, which will never lead to carbon neutrality unless we have significant changes in energy code requirements and a value or cap is placed on greenhouse gas emissions. Gazing into a crystal ball, we could perhaps be persuaded that in 2050, the average building built after 2009 would consume 15 percent of today’s energy (or about a third of what is permitted by current codes).

Real Solutions

We must conclude from this that the 2050 emissions targets cannot be achieved by conservation, refurbishment, and good design alone. The gap must be closed by an increased reliance on clean renewable energy to meet the demand.

An examination of the sources of building related emissions shows that 74 percent of the total CO2 comes from electricity consumption resulting from the extensive use of fossil fuels in the United States to generate electricity. The remaining 24 percent is due to the direct consumption of fossil fuels (coal, oil, and gas) at the building. It is clear from this that the greatest potential to reduce building-related emissions exists in replacing conventional electricity use with power generated from renewable sources.

The annual U.S. greenhouse emissions from electricity generation are 2,433 million tons per year. The total generating capacity is about 1,000 gigawatts (GW), including all sources (although some proportion of this will be down for maintenance at any given time). This suggests an emission rate of 2.4 million tons of CO2 per year for every GW of installed electrical generating capacity.

Our emissions gap is 713 million tons of CO2 per year to be achieved with renewables. Roughly speaking, this indicates that we would need about 300 GW of new generating capacity from renewable energy sources by 2050 to meet the emissions targets for the residential and commercial building sector alone.

This looks like a daunting target. However, if we were to place just 200 square feet of photovoltaic panel on the roof of each of the 120 million dwellings there will be in the United States by 2050, we would get very close to 300 GW of peak generating capacity — when the sun shines. In combination with commercial wind and solar generating stations, 300 GW would be easy to achieve by 2050, at approximately 7.5 GW per year. (A similar amount will be required to offset emissions from the transportation and industrial sectors, giving a total of, say, 15 to 20 GW per year).

The United States added 5.2 GW of new wind generating capacity in 2007, and photovoltaic installations in 2008 amounted to 0.3 GW. This suggests that momentum is building in the renewable energy market, although the level of investment is still at only a third to a quarter of where it needs to be. New legislation on carbon caps being proposed by the Obama administration will surely accelerate this trend if it is enacted.

In summary, a three-pronged approach will allow us to comfortably achieve the 2050 emissions targets:

•    Making all new buildings highly energy efficient
•    Aggressively renovating existing building stock to halve its emissions
•    Moving toward building-integrated renewable energy sources

So there is clearly light at the end of the tunnel. These steps are entirely feasible, and the change in direction will be assisted by any sort of taxation applied to emissions that will provide an economic incentive to move away from business as usual toward conservation and the use of renewable energy. However, the biggest challenge will be the change in mindset required to persuade all of us in the building industry to put in the necessary intellectual effort and investment in the years to come.


Mahadev RamanMahadev Raman leads Arup’s Social Infrastructure business and serves on the firm’s main board. He has been with Arup since 1978, providing engineering design leadership on a wide variety of projects in many countries. Raman was an early pioneer in the use of computational techniques to optimize the performance of low-energy buildings, work he continues with today. He is also a faculty member at Princeton University, where he lectures on sustainable design and environmental control.