This is part two in a pair of stories, adapted from a set of comments published by the author on an online discussion group from October to April. Find part one here.The proposal I support along with more than 150 longtime green builders, "LEEDing on Climate Change," seeks to establish minimum levels of carbon reduction by level for LEED, supports USGBC in its current LEED upgrade and reflects the scientific urgency of climate change. LEED has a critical role to play in solving the biggest threat of our lifetime: climate change and how we stay under 1.5 degrees Celsius.Raising minimum CO2 reductions for LEED would have both positive and negative consequences. On the negative side, building owners seeking a green label with little or no effort to get it might drop out from modest minimum CO2 reductions proposed at the Certified and Silver LEED levels.However, when we added minimum energy performance to LEED, despite concerns that this would reduce growth in LEED, no such slowdown occurred. Our proposal would increase minimum CO2 reductions greatly, only for Gold and Platinum levels, allowing for recognition of moderate CO2 improvements at the Certified and Silver level as well as encouraging real climate change leadership at the Gold and Platinum levels.Raising the minimum CO2 reductions would make the LEED cachet more valuable and motivate more organizations to seek or require a rating. Other green building standards are far stronger on climate change that LEED. New York, Toronto and Vancouver are shifting to adopt the Passivhaus design standard, largely because of this strength. The British green building standard, BREEAM, becoming available in the United States, is a direct competitor to LEED that promotes itself as more rigorous and serious on climate change. Raising the minimum CO2 reductions would make the LEED cachet more valuable and motivate more organizations to seek or require a rating. Our proposal's many supporters advocate broadening the performance range of LEED to include both high minimum CO2 reductions for Gold and Platinum levels while still offering fairly easily achievable, lower levels of LEED. This broadening of climate performance (consistent with the original design intent of LEED) would both attract greater adoption by leading cities and corporations serious about climate change (which are moving away from LEED for its weakness on climate) while protecting USGBC revenue from less-ambitious LEED adherents.Raising CO2 reduction minimums for higher levels of LEED also would accelerate innovation around renewable energy purchase power agreements (PPAs) and similar contracting approaches increasingly being deployed by corporations (PDF). Corporate and institutional direct purchase of clean power continues to accelerate. Intuit, with 2.8 million users, just developed and launched an effort to enable its customers, employees and business partners to buy fractional ownership in new wind-generating projects, allowing deep and cost-effective carbon reductions. The Intuit VP who set this up commented, "It wasn't that hard; it really wasn't." USGBC profitably could facilitate such clean-power contracting for its members.A key, often overlooked issue is LEED's impact on long-term cost curves of deep-green technologies and services. Deep green buildings deploy advanced approaches and technologies, driving down costs. As market demand expands for high-performance technologies — such as electrochromic windows, phase change materials, addressable LED ballasts, extremely high albedo surfaces and carbon sequestering concrete — it has a large cost-reduction impact. As the volume of solar PV doubles, for example, cost drops by around 15 percent (PDF). (The rapid expansion of cost-effective, onsite renewable energy deployment and offsite power purchases also means that LEED no longer should rely on much-derided, zero-impact RECs for LEED buildings.)When we designed LEED, it had no market share, so changes to it had a limited impact on the rate of technology adoption. The capability to accelerate CO2 reductions by bending the cost/volume curve for advanced green products and services may be LEED’s most important and largest lever. LEED already has helped drive these cost reductions.Establishing higher minimum CO2 reductions would better harness LEED's latent power. Because what USGBC does with LEED has broad international impact, higher U.S. LEED CO2 minimums likely would have large CO2 reduction benefits outside the United States in increasingly global product and service markets. Corporate and institutional direct purchase of clean power continues to accelerate, enabling very deep and cost-effective reductions of building and corporate global warming impact. Buildings are the single largest part of the CO2 footprint of most cities and corporations. Today, there is no broadly adopted, rigorous green design standard aggressive on climate change and available to drive and demonstrate deep CO2 reductions in buildings. The obvious choice is LEED.There is no good financial or market reason for LEED not to step up in its current revision process to incorporate the "LEEDing on Climate Change" proposal.The USGBC is considering the adoption of substantial CO2 minimums, as described in the proposal, in its LEED V4.1 upgrade process. These requirements would help to drive the kind of integrated solution LEED was designed to encourage — where, for example, dynamic management of natural lighting, integrated solar shading and advanced controls make for lower CO2, reduced HVAC costs and a more responsive and healthy workspace.One of LEED's great strengths is that it has attracted passionate motivated leaders, including millennials, many of whom no longer view LEED as motivating or leading on climate change. High minimum CO2 reductions for advanced levels of LEED would renew that passion and purpose.