<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><p style="box-sizing: border-box; margin: 1.6rem 0px; font-variant-ligatures: common-ligatures; orphans: 2; widows: 2; background-color: rgb(255, 255, 255);" class=""><em style="box-sizing: border-box;" class=""><a href="https://www.quora.com/What-are-the-major-uncertainties-in-climate-change-projections" target="_blank" style="box-sizing: border-box; background-color: transparent; text-decoration: none; color: rgb(0, 56, 145);" class="">What are the major uncertainties in climate change projections?</a> originally appeared on <a href="http://www.quora.com/" target="_blank" style="box-sizing: border-box; background-color: transparent; text-decoration: none; color: rgb(0, 56, 145);" class="">Quora</a>: </em><em style="box-sizing: border-box;" class="">the place to gain and share knowledge, empowering people to learn from others and better understand the world</em>.</p><p style="box-sizing: border-box; margin: 1.6rem 0px; font-variant-ligatures: common-ligatures; orphans: 2; widows: 2; background-color: rgb(255, 255, 255);" class=""><strong style="box-sizing: border-box;" class=""><a href="https://www.quora.com/What-are-the-major-uncertainties-in-climate-change-projections/answer/Michael-Barnard-14" target="_blank" style="box-sizing: border-box; background-color: transparent; text-decoration: none; color: rgb(0, 56, 145);" class="">Answer</a> by <a href="https://www.quora.com/profile/Michael-Barnard-14" target="_blank" style="box-sizing: border-box; background-color: transparent; text-decoration: none; color: rgb(0, 56, 145);" class="">Michael Barnard</a>, low-carbon innovation analyst, on <a href="http://www.quora.com/" target="_blank" style="box-sizing: border-box; background-color: transparent; text-decoration: none; color: rgb(0, 56, 145);" class="">Quora</a>:</strong></p><p class="qtext_para" style="box-sizing: border-box; margin: 1.6rem 0px; font-variant-ligatures: common-ligatures; orphans: 2; widows: 2; background-color: rgb(255, 255, 255);"><a href="https://www.forbes.com/sites/quora/2017/08/01/what-we-know-and-dont-know-about-climate-change/#42bd2a582513" class="">https://www.forbes.com/sites/quora/2017/08/01/what-we-know-and-dont-know-about-climate-change/#42bd2a582513</a></p><p class="qtext_para" style="box-sizing: border-box; margin: 1.6rem 0px; font-variant-ligatures: common-ligatures; orphans: 2; widows: 2; background-color: rgb(255, 255, 255);">There are a variety of uncertainties in climate change science and projections. For convenience, I'll start with the most certain and proceed to the least certain. And to be clear, climate change is certain, as are negative effects.</p><ol style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; padding-left: 0px; margin: 1.6rem 0px; font-variant-ligatures: common-ligatures; orphans: 2; widows: 2; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class="">The atmosphere is warming. 100% certain.</li><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class="">CO2 traps infrared leaving the Earth, increasing the temperature of the atmosphere. 100% certain.</li><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class="">Methane also traps infrared, in much higher amounts than CO2 but dissipates from the atmosphere much faster. 100% certain.</li><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class="">Humans have increased the parts per million of CO2 in the atmosphere by 67% in the past couple of hundred years. 100% certain.</li><div class="vestpocket" vest-pocket="" style="box-sizing: border-box;"></div><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class="">If CO2 and methane double (which we are closing in on), that locks in 1.0 to 1.2 degrees Celsius. Note the range of uncertainty.</li><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class="">There is a feedback factor with water vapour. More warmth in the atmosphere means more water vapour and water vapour traps even more heat. If CO2 and methane double -- once again, closing in on this -- then the feedback with water vapour results in an additional 1.6 degrees of warming. There's a small range of uncertainty around that and it means we are currently on track for 2.6 to 2.8 degrees of warming if action isn't taken just from CO2, methane and water vapour.</li><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class="">There is a feedback factor with clouds which has a wider range of possible results in the models, from 0.3 degrees to 1.1 degrees with 0.7 degrees being the median. That cloud feedback will increase warming is 100% settled, but the range of the feedback is of lower certainty. That adds up to 2.9 to 3.9 degrees of warming as a range.</li><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class="">There is a median likelihood, given the above, of one meter of sea level rise if we merely stopped adding greenhouse gases to the atmosphere extremely rapidly. There's a fair amount of variance on this, almost all of which is on the really bad side, with news every day of new ice shelves dropping into the sea and feedback effects eliminating more ice currently on land much more rapidly than expected. The science on sea level rise certainly isn't settled except for one part: there is 100% certainly that the sea will rise substantially, it's just a question of whether it's a meter or several meters and whether it's in 80 years or 150 years.</li><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class="">Extreme weather events will increase. That means more droughts, tornadoes, hurricanes, monsoons, floods and the like. That's 100% certain. The degree of increase and the actual numbers vary widely. Where the impacts will be most felt varies substantially. The degree of impact is not settled, but the basics are.</li><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class="">The impact on species, humans, disease spread and the like is almost entirely negative due to the rapidity of change. How severe the impacts will be and where they will be felt specifically has much greater variance.</li><li style="box-sizing: border-box; -webkit-margin-before: 0px; -webkit-margin-after: 0px; margin: 1em 0px 1em 3em; list-style: decimal;" class=""><span class="qlink_container" style="box-sizing: border-box;"><a href="https://www.quora.com/profile/Jim-Seidman" target="_blank" style="box-sizing: border-box; background-color: transparent; text-decoration: none; color: rgb(0, 56, 145);" class="">Jim Seidman</a></span><span style="box-sizing: border-box;" class=""> </span>suggested this good addition: "I would add that there's considerable uncertainty as to the feedback effects on ocean circulation. For example, it's 100% certain that a shutdown of the Atlantic Meridional Overturning Circulation would have terrible consequences for the planet, but it's very hard to predict when or if that might happen."</li></ol><p class="qtext_para" style="box-sizing: border-box; margin: 1.6rem 0px; font-variant-ligatures: common-ligatures; orphans: 2; widows: 2; background-color: rgb(255, 255, 255);">To summarize, it is certain that the atmosphere and oceans are warming due to human greenhouse gas emissions and that this will have negative impacts. The degree of warming has some variance and many of the models are tightly coupled to what humanity chooses to do about it. The degree of and location of impacts are less certain but almost entirely negative.</p><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""></div></div></div><div class="">
<div style="color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); font-family: Verdana; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">--------------------<br class="">"It is solar energy that moves the rabbit, the deer, the whale, the boy on the bicycle outside my window, my pencil as I write these words."<br class=""><br class="">"Only about a tenth of 1 percent of the energy received from the sun by the earth is fixed by photosynthesis .... Worldwide it is about the equivalent to the annual production of between 150 and 200 billion tons of dry organic matter….”<br class=""><br class="">"The worldwide increase of human numbers ... requires that a growing fraction of the total energy fixed be diverted to the direct support of man."<br class=""><br class="">“The broad pattern of these changes is clear enough.”<br class=""><br class="">Woodwell, George. "The Energy Cycle of the Biosphere.” Scientific American. September, 1970<br class=""><br class=""> </div></div></div>
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