While western nations have dropped emissions on schedule, led by the United States, which has pushed its greenhouse gas emissions from energy back to early 1990s levels and coal back to early 1980s levels, the increasingly modern developing world have continued to produce more emissions, causing worldwide levels to rise.

There is no short cut. Emissions need to be reduced. So forget about positioning giant mirrors in space to reduce the amount of sunlight being trapped in the earth's atmosphere or seeding clouds to reduce the amount of light entering earth's atmosphere - if we can't figure out why emissions have risen but temperatures have not, tinkering with clouds is a very bad idea.

Instead, before warming really reaches an inflection point, it's good to think about strategies that can reduce emissions while still insuring that developing nations can have better lives - cars and food and televisions - just like rich countries.

A new report by professors from UCLA and five other universities concludes that there's no way around it: We have to cut down the amount of carbon being released into the atmosphere. The interdisciplinary team looked at a range of possible approaches to dissipating greenhouse gases and reducing warming.

A new UCLA paper in Frontiers in Ecology and the Environment discussed a few geoengineering solutions that can augment efforts to reduce the 9 gigatons of carbon dioxide being released each year by human activity. They reviewed over 100 studies that addressed the various implications of climate engineering and their anticipated effects on greenhouse gases. 

They focused on five strategies that are discussed the most: reducing emissions, sequestering carbon through biological means on land and in the ocean, storing carbon dioxide in a liquefied form in underground geological formations and wells, increasing the Earth's cloud cover and solar reflection. 

Of those approaches, none of the estimated benefits came close to reducing emissions as much as conservation, increased energy efficiency and low-carbon fuels might. Technology that is already available could reduce the amount of carbon being added to the atmosphere by some 7 gigatons per year, the team found. 

We have discussed this many times on Science 2.0. While it is politically fashionable to subsidize solar panels on the homes of rich people, and making Chinese companies wealthy doing it, a far better solution would have been to spend the tens of billions of dollars wasted on subsidies and mandates in the last 5 years on making existing buildings - such as older apartments and businesses - more energy efficient.

Sequestering carbon through biological means — converting atmospheric carbon into solid sources of carbon like plants — holds the most promise, at least if cost is no object, since only rich countries are going to do it and rich countries are already reducing emissions. Adding new forests, could tie up as much as 1.3 gigatons of carbon in plant material annually, the team calculated but that may not be feasibale. Deforestation now is responsible for adding 1 gigaton of carbon each year to the atmosphere but that is primarily happening in the developing world. The US alone has more untouched natural land than the entire continent of Africa.

This uncontroversial change would help a lot 

Improving soil management would really make a big difference. Soils can trap plant materials that have already converted atmospheric carbon dioxide into a solid form as well as any carbon dioxide that the solids give off as they decompose. Since the dawn of agriculture, tilling land has led to the loss of about half (55 to 78 gigatons) of the carbon ever sequestered in soil, the team reports. Simple steps as leaving slash — the plant waste left over after crop production — on fields after harvests, could be incorporated into the soil and reintroduce between 0.4 and 1.1 gigatons of carbon annually to soil, the study says.

The approach would also improve soil's ability to retain nutrients and water, making it beneficial for additional reasons. 

"Improved soil management is not very controversial," says Daniela Cusack, the study's lead author and an assistant professor of geography in UCLA. "It's just a matter of supporting farmers to do it."

They also advocate a less familiar form of biological sequestration: the burial of biochar. This process uses high temperatures and high pressure to turn plants into charcoal and releases little carbon dioxide into the atmosphere. Under normal conditions, decaying plant life inevitably decomposes, a process that releases carbon dioxide into the atmosphere. But charred plant material takes significantly longer — sometimes centuries — to decompose. So the approach can work to keep carbon that has become bound up in plant life from decaying and respiring as carbon dioxide. And like working slash into the soil, adding biochar to soil can improve its fertility and water retention.  It's an expensive proposition, though.

"Charcoal has been used as an agricultural amendment for centuries, but scientists are only now starting to appreciate its potential for tying up greenhouse gases," Cusack said.

Not all biological sequestration would be so beneficial. The researchers evaluated the idea of adding iron to oceans in order to stimulate the growth of algae, which sequesters carbon - a few years ago a group of scientists led by Germany violated international law and began a large experiment with creating large algal blooms.  Germans tend to not like laws they don't create, almost every time someone tries to hijack the Science 2.0 name to make money, it is in Germany. It's little surprise that they have embraced their idea of dumping iron into the oceans even though it is the least viable strategy. Less than a quarter of the algae could be expected to eventually sink to the bottom of the ocean, which would be the only way that carbon would be sequestered for a long period of time.The rest would be consumed by other sea life that respire carbon dioxide, which would end up back in the atmosphere anyway, along with wreaking havoc by decreasing the oxygen available for other marine life. 

They believe, at least based on papers that they reviewed, that carbon capture and storage would work, particularly when the technique is used near where fuels are being refined - but it is the least politically viable option. The US President won't even make a decision to consider Yucca Mountain, which scientists studied for 25 years and repeatedly declared safe for nuclear waste. If America can't even find a way to store nuclear waste, which is guaranteed to work, there is no way storing carbon with its unknown cost, is going to happen. Carbon capture and storage  turns carbon dioxide into a liquid form of carbon, which oil and coal extraction companies would then pump into underground geological formations and wells and cap; millions of tons of carbon are already being stored this way each year. And the approach has the potential to store more than 1 gigaton permanently each year — and up to 546 gigatons of carbon over time — the study says. Yet who have environmental groups and popular media chosen to demonize about energy? Fossil fuel companies, who will be expected to do all of this as another tax

And environmentalists won't allow it even if fossil fuel companies would be forced to pay for it. They don't even like safe pesticides, there is no way they would not object to a potential liquid carbon leak that would be fatal to humans and other animals.

"With CCS we're taking advantage of an approach that already exists, and big companies pay for the work out of their own pockets," Cusack said, with a delightful lack of knowledge about how economics works. "The hurdle is public perception. No one wants to live next to a huge underground pool of carbon dioxide that might suffocate them and their children – no matter how small the risk."  

There are other options. Germany is abandoning its solar power schemes, which has caused numerous Chinese solar panel manufacturers to declare bankruptcy - and are trying to embrace fracking. While solar power is not ready yet, and won't be no matter how much money we throw at it today, it will be eventually. There is also the potential of fusion, though that is not even close either. Nuclear energy remains the cleanest bridge to those sources but it is politically unviable in the US and Europe today. Natural gas remains the best short-term way to reduce emissions. And that would help in the developing world also.