( CNN ) -- When climate scientist Rosina Bierbaum speaks , her central theme is the `` roasted world '' -- a bleak picture of what the planet will probably look like if carbon pollution continues unchecked , leading to 4 degrees Celsius of warming by mid-century . Four degrees may not sound like a lot -- but it would change our lives drastically . Mega-heat waves in 2010 in Europe and Russia were estimated to have caused up to 50,000 heat-related deaths , according to some reports . This `` will become the normal , '' said Bierbaum , a review editor of the United Nations ' Intergovernmental Panel on Climate Change report , speaking at the U.N. in January . Food production in key regions such as sub-Saharan Africa and South Asia could drop by as much as 50 % , she added . Accelerated melting of the Greenland and Antarctica ice sheets will cause sea levels to rise by 1 to 2 feet , putting Miami and Mumbai , India , as well as many other low-lying cities , at enormous risk . It 's a bone-chilling scenario . We do n't always have control of our destiny , but in the case of climate change we know exactly what it will take to protect our planet and economy from disaster . Companies , investors and policymakers must scale up clean energy investments and scale down fossil fuel investments . Recently , we saw compelling evidence that big business is getting more serious about climate change . And it came from none other than the world 's largest fossil fuel company , Exxon Mobil . Nearly 25 years to the day after the Exxon Valdez supertanker ran aground in Alaska , spewing 260,000 barrels of crude oil , Exxon has agreed to report to investors on how climate change will affect its core business model , including the prospect that major portions of its oil reserves may need to be left in the ground as carbon-reducing policies and expanded use of renewable energy take hold globally . U.S. oil production since Exxon Valdez . I remain guarded about how major oil companies will ultimately transition to being energy companies rather than fossil fuel companies , boosting our economy sustainably rather than pushing it closer to a breaking point . But Exxon 's commitment reflects a growing consensus among business leaders and investors that climate change is a core economic risk that must be tackled now . This is in stark contrast to just a few years ago , when climate change was seen as a tree-hugger issue relevant more to polar bears than financial bottom lines . After years of foot-dragging , businesses are recognizing the scientific certainty and economic effects of climate change -- from higher food costs to broken supply chains to costlier weather-related disasters . They see the powerful dollars-and-cents argument for mitigating carbon pollution today rather than waiting until it is too late and too expensive . Companies such as General Motors , Apple and Starbucks are now calling for strong climate and clean-energy policies in Congress . They are among more than 750 companies that have signed Ceres ' Climate Declaration , which brings together companies and individuals to demonstrate support for national action on climate change . The world 's largest institutional investors -- including many of the 500 that attended the U.N. Investor Summit on Climate Risk -- are actively integrating climate risks and opportunities into their investment decisions . Some are already pulling out of riskier carbon-intensive investments such as coal companies and are setting specific targets for elevating clean energy investments . Major stock exchanges are also beginning to require listed companies to disclose climate and other sustainability risks to investors . And securities regulators , including the U.S. Securities and Exchange Commission and state insurance regulators , have taken strong steps , at Ceres and investors ' urging , to require similar climate risk disclosure . These actions are profoundly important if we are to have any hope of thwarting , or limiting , the impact of this colossal global threat , which requires a massive shift in our economy to clean energy and away from fossil fuels . Solving climate change and building a sustainable global economy can not happen unless companies and investors realize their role in the problem and become part of the solution . We are making progress . Yet even as the biggest companies in the world change their business practices and come out in support of strong climate action , it remains a deeply controversial issue in Washington , which has led to policy paralysis . It is unfathomable . We must demand a vigorous debate over how best to meet the climate challenge , casting climate deniers out to the fringe where they now belong . Unless we act now , the threat that climate change poses to the planet will be exponentially greater . And the solutions will be increasingly harder to implement down the road . The `` roasted world '' warning is a real threat , but it does n't need to become our reality . The opinions expressed in this commentary are solely those of Mindy Lubber .
today , the Exxon Valdez supertanker created a gigantic oil spill in Miami waters . Rosina Bierbaum : Top companies such as the United Nations ' Intergovernmental Panel on Climate Change are ready to act on climate change . She says businesses realize how carbon pollution drags down their bottom lines . Lubber : If they do n't embrace clean energy now , it may be too late and too expensive .