Heads of state and corporate chiefs who converged in Abu Dhabi last week for the World Future Energy Summit repeated one question: where's the money?
The renewable energy and power efficiency initiatives many agree can help the world avoid the worst effects of climate change require funding - but money invested in fossil fuels continues to outstrip that spent on low-carbon alternatives.
The financial downturn has squeezed renewable energy projects, trimming demand for wind turbines, while the near-term solar future is clouded by cuts in European subsidies in countries including Spain.
Publicly traded alternative energy companies suffered last year, with an international index of such firms falling by 14.6 per cent compared with 2009.
"One thing that's required is continuous investments … We've invested sporadically," said Dr Susan Hockfield, the president of the Massachusetts Institute of Technology, on the sidelines of the summit. "Renewables probably have a couple of decades to go."
Dr Hockfield and others say that in the coming decades, governments would need to put up cash for academic research and corporate investment in renewable energy. They have a long way to go.
Direct subsidies for renewable energy and biofuels came to between US$43 billion (Dh157.92bn) and $46bn last year, less than 10 per cent of the $557bn that went to fossil fuels, according to Bloomberg analysts.
But other sources of funding for renewables are increasing. Investment in wind, solar and biofuels was up last year from 2009, including from venture capital and private equity firms.
"The pace of change has to be stronger, and the policy has to be more reliable," said Dr Nicholas Stern, who heads the Grantham Research Institute on Climate Change and the Environment at the London School of Economics.
"How much will it cost? A good deal less than we spend on fossil fuels now."
Below, we answer a few big questions about the future of clean energy.
q Who cares?
a Renewables can help address global energy inequality. Between 1.4 billion and 1.6 billion people lack access to electricity, with total use in sub-Saharan Africa about equal to that of New York City.
"This is not a joke," said Dr Fatih Birol, the chief economist at the International Energy Agency based in Paris. "This is a serious issue in terms of the economy."
Solar power and other renewable energy sources in rural regions can help bridge that gap, experts say. Bringing energy to the have-nots and reducing use among the haves will help address the inter-linked issues of poverty, public health and women's rights, said Ban Ki-moon, the UN secretary general.
"We need a global clean energy revolution," Mr Ban said.
Although renewables are set to occupy an increasing share of the world's electricity market, that growth may not be as fast as Mr Ban would like.
Renewable sources supply 19 per cent of the world's electricity today and, according to analysts' estimates, will make up one third of global supply in 2035.
q How much will it cost?
a At least US$6 trillion (Dh22.03tn) must be invested into renewable energy research and projects over the next quarter decade if the world wants to avoid a climate crisis, Dr Birol said.
The US, Europe and China will lead investments. East Asia , however, is likely to play a more ambiguous role in climate change efforts as it fuels its economic expansion with a cocktail of coal and renewables. Over the next 25 years, China's coal-fired power plants will account for one third of global carbon dioxide emissions growth. But the country is expected to also lead the world in renewable energy growth in the next 25 years, bringing online 85 gigawatts (gw) of solar photovoltaic solar power, 335gw of wind power, and 8.5 million electric and hybrid cars. China's additions to wind power capacity will account for more than a quarter of the world's increase, experts predict.
q What about international regulation?
a Government leaders are now looking to nations to lead their own efforts, rather than global agreements such as those being brokered at talks sponsored by the UN.
"I don't think it's wise to reply on the international climate procedure to be a panacea for how we undertake national policy," said Dr Morgan Bazilian, a special adviser on energy and climate change at the UN Industrial Development Organisation. Leaders from Mr Ban to heads of state now hope national policies can foster the renewables investment that international agreements have not.
"Five years ago everyone was looking for global negotiations," said Olafur Ragnar Grimsson, Iceland's president, on the sidelines of the summit in Abu Dhabi. "Now each country is doing its own action. It serves their economic interest to act now rather than wait for global negotiations. And that's a good thing." Changes to national policy are under consideration in the Gulf region, but reducing oil and gas subsidies across the board unilaterally would eliminate a key competitive advantage.
q Where are the investors?
a The international finance community holding the money that could back renewables growth still considers the sector relatively risky. Government policy can mitigate that risk, but investors are reluctant to rely on government action that could be recalled at any time.
"There's a general level of amazement about the complete incompetence that's gone into policy-making in this space," said Alex O'Cinneide, the general manager of Masdar Capital, Abu Dhabi's sustainable energy investment arm. "What we find hard to handle is not knowing how risk and return will be balanced."
q Are government subsidies necessary?
a Government subsidies may not be sustainable in the long term and can be tricky to balance as Spain has shown recently. Robust carbon credit trading modelled after traditional commodities markets could allow renewable energy and conservation projects to take off.
"If there was a carbon market, different measures like this would definitely help renewable energies to become more competitive, less government support would be needed and more doors would be open for renewable energy," Dr Birol said.
Carbon markets already exist. But prices, which tend to fall amid uncertainty about government policy and international talks, must be helped to rise to make alternative energy projects profitable without government incentives, analysts say.
"There has to be a cost of doing things dirty," Dr Stern said.
q Will renewable energy investment be enough to curb climate change?
a Energy leaders are getting to grips with the idea that renewables may not be enough to lower carbon dioxide emissions. They are looking to efficiency measures, nuclear power and carbon burial to bridge the gap.
"Energy must come from a mix of sources - a mix that will also include clean fossil fuels, peaceful nuclear energy and, of course, renewable energy," said Dr Sultan al Jaber, the chief executive of Masdar, Abu Dhabi's clean energy company. "Competition drives innovation."
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