The environmental benefits of renewable energy technologies are widely recognised, but the contribution that they can make to energy security is less well known. Renewable technologies can enhance energy security in electricity generation, heat supply, and transportation. Energy security Access to cheap energy has become essential to the functioning of modern economies. However, the uneven distribution of fossil fuel supplies among countries, and the critical need to widely access energy resources, has led to significant vulnerabilities. Threats to global energy security include political instability of energy producing countries, manipulation of energy supplies, competition over energy sources, attacks on supply infrastructure, as well as accidents and natural disasters. Energy security, therefore, has become fundamental from many perspectives, and is being therefore increasingly at the centre of legal and policy issues linked to social, economic, and development matters. The Fukushima I nuclear accidents in Japan have brought new attention to how national energy systems are vulnerable to natural disasters, with climate change already bringing more weather and climate extremes. These threats to our old energy systems provide a rationale for investing in renewable energy. Shifting to renewable energy "can help us to meet the dual goals of reducing greenhouse gas emissions, thereby limiting future extreme weather and climate impacts, and ensuring reliable, timely, and cost-efficient delivery of energy". Investing in renewable energy can have significant dividends for our energy security. Transportation The International Energy Agency's World Energy Outlook 2006 concludes that rising petroleum demand, if left unchecked, would accentuate vulnerability to a severe supply disruption and resulting sudden price increases, in consuming countries. Renewable biofuels for transport represent a key source of diversification from petroleum products. Biofuels from grain and beet in temperate regions have a role, but they are relatively expensive and their energy efficiency and carbon dioxide savings, vary. Biofuels from sugar cane and other highly productive tropical crops are much more competitive and beneficial. But all first generation biofuels ultimately compete with the production of food for land, water, and other resources. More effort is required to develop and commercialize second generation biofuel technologies, such as biorefineries and cellulosic ethanol, enabling the flexible production of biofuels and related products from non-edible parts of the plant. According to the International Energy Agency (IEA), cellulosic ethanol commercialization could allow ethanol fuels to play a much larger role in the future than previously thought. Cellulosic ethanol can be made from plant matter