This month, the Intergovernmental Panel on Climate Change will begin releasing its fifth assessment report. Like earlier reports, it will undoubtedly lead to more calls to reduce emissions of carbon dioxide worldwide.

As the discussion unfolds, I would urge everyone to keep four numbers in mind: 32, 1, 30 and 1/2. These are the numbers that explain why any transition away from our existing energy systems will be protracted and costly. Let's take them in sequence.

First, 32: That's the percentage growth in carbon dioxide emissions that has occurred globally since 2002. In the past decade, these emissions have increased by about 8.4 billion tons. And nearly all of that has happened in the developing world. In Asia, emissions rose 86 percent; in the Middle East, 61 percent; and in Africa, 35 percent.

In the U.S., meanwhile, carbon dioxide emissions were 8 percent lower in 2012 than they were in 2002, largely due to a surge in shale gas production, which has reduced coal use. In Europe, carbon dioxide emissions have been essentially flat for a decade.

That 32 percent increase in global carbon dioxide emissions reflects the central tension in any discussion about cutting the use of coal, oil and natural gas: Developing countries -- in particular, fast-growing economies such as Vietnam, China and India -- simply cannot continue to grow if they limit the use of hydrocarbons. Those countries' refusal to enact carbon taxes or other restrictions illustrates what Roger Pielke Jr., a professor of environmental studies at the University of Colorado, calls the "iron law of climate policy": Whenever policies "focused on economic growth confront policies focused on emissions reduction, it is economic growth that will win out every time."

Over the past 10 years, despite great public concern, carbon dioxide emissions have soared because some 2.6 billion people still live in dire energy poverty. More than 1.3 billion have no access to electricity at all.

Now to the second number: 1. That's the power density of wind in watts per square meter. Power density is a measure of the energy flow that can be harnessed from a given area, volume or mass. Six different analyses of wind (one of them is my own) have all arrived at that same measurement.

Wind energy's paltry power density means that enormous tracts of land must be set aside to make it viable. And that has spawned a backlash from rural and suburban landowners who don't want 500-foot wind turbines near their homes. To cite just one recent example, in late July, some 2,000 protesters marched against the installation of more than 1,000 wind turbines in Ireland's Midlands Region.

Consider how much land it would take for wind energy to replace the power the U.S. now gets from coal. In 2011, the U.S. had more than 300 billion watts of coal-fired capacity. Replacing that with wind would require placing turbines over about 116,000 square miles, an area about the size of Italy. And because of the noise wind turbines make -- a problem that has been experienced from Australia to Ontario -- no one could live there.

And:

Now let's turn to the third number: 30. This represents the massive scale of global energy use, which is about 250 million barrels of oil equivalent per day, or the output of about 30 Saudi Arabias. (Since the 1970s, the Saudis have produced about 8.2 million barrels of oil per day.) Of that 30 Saudi Arabias of daily energy consumption, we get 10 from oil, nine from coal, seven from natural gas, two from hydro and 1 1/2 from nuclear.

That remaining 1/2 -- the final number -- represents the amount of energy we get from all renewable sources, not counting hydropower. In 2012, the contribution from all of those sources amounted to about 4.8 million barrels of oil equivalent per day, or roughly one-half of a Saudi Arabia. Put another way, we get about 50 times as much energy from all other sources -- coal, oil, natural gas, nuclear and hydropower -- as we do from wind, solar, geothermal and biomass.

David Fuller's view If we are going to reduce global carbon dioxide emissions anytime soon, meaning within the next five to ten years, countries need to take two important steps: 1) Increase the production of natural gas which exists within shale formations in most countries; 2) Build new nuclear power stations.

Unfortunately, these are hard sells, although that does not justify giving up the effort. Energy production is always a 'NIMBY' issue, particularly in developed countries. People oppose fracking anywhere near where they live, often citing water pollution. However this risk has been considerably reduced in the USA, so the real reasons are fears that the drilling operations will desecrate the countryside and lower property values. For developing countries, only fracking has a chance of competing with the cost of coal.

New nuclear is far safer than the old Fukushima plants but it is probably the 'hardest sell' of all. This is mainly due to the Fukushima accident triggered by a huge tsunami in March 2011. However, the bigger problem concerns nuclear waste from spent fuel. To date, there is no solution to this problem other than very long-term storage which is expensive and unsatisfactory. Nevertheless, new technologies still in the planning stage have the potential to greatly reduce nuclear risks while also producing less toxic waste, as you will see from the article below.