The risks of climate change and, of course, high oil prices have unleashed a wave of interest and commitment to changing our energy economy that, perhaps, could safeguard the planet. City, state, federal and international proposals and legislation are today all in play -- and in flux -- to lay out targets for greenhouse gas reductions.

Some of the most notable are the 25 percent reduction in GHG emissions by 2025 and the 80 percent reduction by 2050 that California has adopted, the 70 percent or more reductions proposed in the United Kingdom, New Zealand, and the Japanese proposals, and the 100 percent fossil-fuel-free plans of Sweden, and a number of progressive cities intent on making climate-wise statements.

How these diverse and ambitious plans pan out is anybody's guess -- or more accurately a guess for some, and a hope for us all. The U.N.'s Intergovernmental Panel on Climate Change (IPCC) is a several-decade collaboration of several thousand scientists from around the planet, with the objective of evaluating the state of not only the science of climate change, but also -- and increasingly importantly -- the efficacy of approaches to GHG emissions reduction and, sadly, adaptation.

Politics at least partially aside, the share of the Nobel Peace Prize for 2007 awarded to the IPCC is a major step in acknowledging the need for shared recognition of the implications of climate change, and the potential for solutions. What we do with that evolving collective wisdom remains to be seen.

As a wide and increasingly loud series of voices and analysts attest, low-carbon energy options abound, ranging from ever more aggressive (and tremendously cost-effective) energy efficiency to renewable energy technologies, to voluntary schemes and low-carbon energy mandates for both stationary and mobile power, to technologies to offset carbon emissions from the fossil-fuels we either must or choose to consume. The increased attention that every aspect of a (potential) clean energy economy is now receiving is, however, not without precedent.

Following the OPEC energy crises and embargoes of the 1970s and early 1980s, energy was also the topic of the day. Federal energy research budgets tripled (only to decline to levels lower than even prior to the crises when oil prices then fell several years later); prospects for diversification off of imported oil seemed possible (today we are more reliant on imported oil than at any time in history); and discussions even began over the need to integrate energy security arguments with a diverse set of approaches to the wider issues of environmental and social sustainability.

We are now in a seemingly similar situation -- except that an increasingly diverse set of arguments are coming together to reinforce the notion that the current focus on energy issues is not like the last one. Today, increasing global competition over energy resources, increasing clarity on climate change, and $90-per-barrel oil prices that a growing number of experts do not expect to ever decline to "pre-rise" levels of $20 to 30 a barrel.

In the face of all this, as more and more municipalities commit to reductions, however, our ability to meaningfully assess our options has not progressed sufficiently. Things are by no means awful, and many useful methods and models do exist to forecast future fossil-fuel prices, estimate the potential growth rate of a wide range of technologies, and to assess feedbacks between economic policies, market and behavioral economics responses, and responses to potentially lurking abrupt climatic or geopolitical change.

Over the past decades a number of assessment frameworks have proven to be particularly useful, revealing, or even defining at various times. Theories of the linearity and law-like dependence of economic growth on energy use we at one stage seen as fundamental. The complexity of energy supply options and end-uses in the economy was often reflected and represented by input-output "spaghetti" diagrams.

The potential for energy efficiency to play a defining role in energy planning was central to the ideas of "soft" and "hard" energy paths (as coined by Amory Lovins in his transformative Soft Energy Paths work in the 1970s), and to the avoided energy (and emissions) analyses central to a generation of demand forecasts by California energy planners. The need to reflect climate, energy and economic interconnections also led to the interest in the diverse types of integrated assessment models.

Figure 1: Cost of avoided carbon graph (Vattenfall Group, Sweden).

So, where do we go to look for functionally useful frameworks?

With the need to respond to climate, energy security, health, challenges now part of the standard dialog, we need frameworks that move beyond lists of solutions. We now need ways to not only look at what different solutions may cost (or pay us back for some investments), how they interact (e.g. hydropower and wind are complementary in many respects, while energy efficiency complements all investments in green power generation), and what portfolio has the potential to achieve what level of climate protection.

Enter an analysis of the cost/benefit of avoided carbon emission produced by the Vattenfall group, the Swedish utility collective, and shown in the figure. Note a whole number of things about his remarkable graph (Figure 1):

• It shows both estimated costs (some are negative) of potential climate solutions, and the amount of carbon they may be able to offset, or avoid, by a specific time (in this case 2030)
• It provides a clear message that if you accept their analyses (many do not agree on the height or width of individual bars, myself included), there are few "home runs," but many, many singles, doubles, and triples out there. We will need them all.
• It gives a foundation for the more complex analysis still needed, both on how different slices interact (something my research group is working on), what is the opportunity cost of investments in one area versus another, and what are the risks of different mitigation and adaptation options (something the graph does not clearly show, but which is implicit in the size of each chunk of the graph)
• It provides a Maginot line (in a good sense!): to arrest greenhouse gas concentration build-up in the atmosphere of, say 550 ppmv one need only go out a certain length on the graph (based on the IPCC models, to about 15 to 20 Euros per ton of carbon equivalent (E/tCO2e), while to control atmospheric GHG levels further, requires investments further out the graph (Figure 2).

Figure 2: Abatements cost estimates for different climate protection levels. 450 parts per million of CO2 in the atmosphere by volume is an optimistic, but potentially necessary level of protection.

The size, both height and width of each bar needs far more work, to be sure, but the power of this analysis is striking.

I will be writing more about this approach in future.

Green-Biz Editor-at-Large Daniel M. Kammen is the Class of 1935 Distinguished Professor of Energy at the University of California. He co-directs the Berkeley Institute of the Environment (http://bie.berkeley.edu) and is founding director of the Renewable and Appropriate Energy Laboratory (http://rael.berkeley.edu). He has appointments in the Energy and Resources Group and the Goldman School of Public Policy.