Welcoming the G8 calls for action, the International Energy Agency warned that at least four times more cash needs to be invested in efficiency and clean energy than pledged so far.
The Paris-based agency said it had calculated that of the total $2.6 trillion of public spending in short-term economic stimulus packages announced to date, $100 billion have been directed at energy efficiency and clean energy.
"This is a step in the right direction. But, much more needs to be done," the IEA's Executive Director Nobuo Tanaka said in a statement.
"Investment in energy efficiency and clean technologies would need to increase four-fold if we want to keep the rise in global average temperature under 2 degrees Celsius (3.6 Fahrenheit). This means $400 billion more every year over the next 20 years."
The G8 agreed on Wednesday to try to limit global warming to 2 degrees Celsius and cut its greenhouse gas emissions by 80 percent, but failed to persuade China and India to join in a bid to halve world emissions by 2050.
The draft text of the G8 has also referred to the need to tackle volatility in energy markets, which it said undermined the ability of industry to plan and invest.
The IEA has consistently warned the present environment of weaker prices and limited credit will hobble investment in new energy supplies, potentially leading to a fresh oil price spike that could disrupt any economic recovery.
It said the G8 call for increased investment in energy supply, energy efficiency and low-carbon technology was "timely and urgent".
"At a time of widespread uncertainty, governments can and must lead the way through increased energy diversification and most importantly, improved energy efficiency, both of which can reduce oil market tightness and volatility," the statement quoted Tanaka as saying.
IEA calculations have shown global investment in upstream oil and gas has already been cut by 21 percent this year compared to 2008 -- a reduction of about $100 billion.
"To reduce excessive volatility of prices and lower investment risks, we urge governments to adopt transparent, stable policies to promote energy investment and to improve their regulation of futures markets," said Nobuo Tanaka.
"And, together we must ensure that sound long-term energy investment strategies are at the heart of every economic stimulus package".