{"id":165,"date":"2009-09-25T09:50:06","date_gmt":"2009-09-24T21:50:06","guid":{"rendered":"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the_greenhouse_effect\/"},"modified":"2009-09-25T09:50:06","modified_gmt":"2009-09-24T21:50:06","slug":"the-greenhouse-effect","status":"publish","type":"post","link":"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/","title":{"rendered":"The greenhouse effect"},"content":{"rendered":"<p>I&#8217;ve been reading in <a target=\"_blank\" href=\"http:\/\/physicsworld.com\/cws\/article\/indepth\/40222\">PhysicsWorld<\/a> about some grand ideas for controlling the earth&#8217;s climate by engineering on a global scale. Some sound pretty fanciful, though some might be just plausible.&nbsp;But before I get there (which will probably be another entry) I think it&#8217;s worthwhile reminding you what the greenhouse effect actually is. As in, why is it a greenhouse gets hot, and what has this got to do with the atmosphere?<\/p>\n<p><!--more--><\/p>\n<p>Let&#8217;s take the greenhouse first of all. Just a few pieces of glass enclosing&nbsp;your tomato plants. Why is it so hot in there? The sun emits a lot of radiation. Because it&#8217;s so hot (around&nbsp;5500 degrees celcius&nbsp;or so) a substantial fraction of its energy it emits at wavelengths in the visible spectrum. When this light arrives at the surface of the earth (let&#8217;s ignore the atmosphere for now) it travels through the glass of our greenhouse and hits the ground \/ tomatos or whatever is in there, where some of it is absorbed. This&nbsp;generates heat,&nbsp;which heats up the&nbsp;material inside.&nbsp;<\/p>\n<p>However, as we know, hot&nbsp;things radiate&nbsp;the heat again. But, unlike the sun, which radiates&nbsp;hugely in the&nbsp;visible spectrum,&nbsp;things at say 20&nbsp;or&nbsp;30 Celcius radiate&nbsp;mostly&nbsp;at infra-red wavelengths. And <b>at infra-red, unlike visible, glass is opaque<\/b>.&nbsp;&nbsp;So the radiated heat can&#8217;t escape. (It can enter, but not leave, because it tries to leave at a different wavelength from what it arrives). Contrast this with the case of no greenhouse &#8211; the light from the sun falls on the ground &#8211; the ground heats up, but this heat can now escape back upwards as it is radiated. It doesn&#8217;t get so hot.<\/p>\n<p>Now let&#8217;s go to the atmosphere. Water vapour and carbon dioxide molecules (amongst others) in the atmosphere do a similar thing to glass. They let visible light through, but absorb infra-red light. The sunlight makes it to the surface, but the heat radiated from the surface gets trapped.&nbsp;Same mechanism as the greenhouse, hence the name greenhouse effect.<\/p>\n<p>NB The different properties of materials at infra-red and visible wavelengths are often overlooked.&nbsp;Paint is&nbsp;a good example &#8211; I often hear people remark that radiators should be painted black to maximise the amount they radiate (black bodies radiate well.) The argument doesn&#8217;t hold because pretty well any colour paint you buy is close to &#8216;black&#8217; if you look at it in infra-red &#8211; i.e. it absorbs (and hence radiates) infra-red radiation (heat) very well. There is no need to repaint your radiators.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I&#8217;ve been reading in PhysicsWorld about some grand ideas for controlling the earth&#8217;s climate by engineering on a global scale. Some sound pretty fanciful, though some might be just plausible.&nbsp;But before I get there (which will probably be another entry) I think it&#8217;s worthwhile reminding you what the greenhouse effect actually is. As in, why [&hellip;]<\/p>\n","protected":false},"author":20,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[9,8],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v22.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>The greenhouse effect : Physics Stop<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"The greenhouse effect : Physics Stop\" \/>\n<meta property=\"og:description\" content=\"I&#8217;ve been reading in PhysicsWorld about some grand ideas for controlling the earth&#8217;s climate by engineering on a global scale. Some sound pretty fanciful, though some might be just plausible.&nbsp;But before I get there (which will probably be another entry) I think it&#8217;s worthwhile reminding you what the greenhouse effect actually is. As in, why [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/\" \/>\n<meta property=\"og:site_name\" content=\"Physics Stop\" \/>\n<meta property=\"article:published_time\" content=\"2009-09-24T21:50:06+00:00\" \/>\n<meta name=\"author\" content=\"Marcus\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Marcus\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"2 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/\",\"url\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/\",\"name\":\"The greenhouse effect : Physics Stop\",\"isPartOf\":{\"@id\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/#website\"},\"datePublished\":\"2009-09-24T21:50:06+00:00\",\"dateModified\":\"2009-09-24T21:50:06+00:00\",\"author\":{\"@id\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/#\/schema\/person\/34d359280e44f926f2df12eb3e50aa22\"},\"breadcrumb\":{\"@id\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/#breadcrumb\"},\"inLanguage\":\"en-NZ\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/\"]}]},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"The greenhouse effect\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/#website\",\"url\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/\",\"name\":\"Physics Stop\",\"description\":\"A light-hearted look at everyday physics going on in the world, written by a physicist but intended for a general audience.\",\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/?s={search_term_string}\"},\"query-input\":\"required name=search_term_string\"}],\"inLanguage\":\"en-NZ\"},{\"@type\":\"Person\",\"@id\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/#\/schema\/person\/34d359280e44f926f2df12eb3e50aa22\",\"name\":\"Marcus\",\"url\":\"https:\/\/blog.waikato.ac.nz\/physicsstop\/author\/mtwilson\/\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"The greenhouse effect : Physics Stop","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/","og_locale":"en_US","og_type":"article","og_title":"The greenhouse effect : Physics Stop","og_description":"I&#8217;ve been reading in PhysicsWorld about some grand ideas for controlling the earth&#8217;s climate by engineering on a global scale. Some sound pretty fanciful, though some might be just plausible.&nbsp;But before I get there (which will probably be another entry) I think it&#8217;s worthwhile reminding you what the greenhouse effect actually is. As in, why [&hellip;]","og_url":"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/","og_site_name":"Physics Stop","article_published_time":"2009-09-24T21:50:06+00:00","author":"Marcus","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Marcus","Est. reading time":"2 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"WebPage","@id":"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/","url":"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/","name":"The greenhouse effect : Physics Stop","isPartOf":{"@id":"https:\/\/blog.waikato.ac.nz\/physicsstop\/#website"},"datePublished":"2009-09-24T21:50:06+00:00","dateModified":"2009-09-24T21:50:06+00:00","author":{"@id":"https:\/\/blog.waikato.ac.nz\/physicsstop\/#\/schema\/person\/34d359280e44f926f2df12eb3e50aa22"},"breadcrumb":{"@id":"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/#breadcrumb"},"inLanguage":"en-NZ","potentialAction":[{"@type":"ReadAction","target":["https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/"]}]},{"@type":"BreadcrumbList","@id":"https:\/\/blog.waikato.ac.nz\/physicsstop\/2009\/09\/25\/the-greenhouse-effect\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/blog.waikato.ac.nz\/physicsstop\/"},{"@type":"ListItem","position":2,"name":"The greenhouse effect"}]},{"@type":"WebSite","@id":"https:\/\/blog.waikato.ac.nz\/physicsstop\/#website","url":"https:\/\/blog.waikato.ac.nz\/physicsstop\/","name":"Physics Stop","description":"A light-hearted look at everyday physics going on in the world, written by a physicist but intended for a general audience.","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/blog.waikato.ac.nz\/physicsstop\/?s={search_term_string}"},"query-input":"required name=search_term_string"}],"inLanguage":"en-NZ"},{"@type":"Person","@id":"https:\/\/blog.waikato.ac.nz\/physicsstop\/#\/schema\/person\/34d359280e44f926f2df12eb3e50aa22","name":"Marcus","url":"https:\/\/blog.waikato.ac.nz\/physicsstop\/author\/mtwilson\/"}]}},"_links":{"self":[{"href":"https:\/\/blog.waikato.ac.nz\/physicsstop\/wp-json\/wp\/v2\/posts\/165"}],"collection":[{"href":"https:\/\/blog.waikato.ac.nz\/physicsstop\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.waikato.ac.nz\/physicsstop\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.waikato.ac.nz\/physicsstop\/wp-json\/wp\/v2\/users\/20"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.waikato.ac.nz\/physicsstop\/wp-json\/wp\/v2\/comments?post=165"}],"version-history":[{"count":0,"href":"https:\/\/blog.waikato.ac.nz\/physicsstop\/wp-json\/wp\/v2\/posts\/165\/revisions"}],"wp:attachment":[{"href":"https:\/\/blog.waikato.ac.nz\/physicsstop\/wp-json\/wp\/v2\/media?parent=165"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.waikato.ac.nz\/physicsstop\/wp-json\/wp\/v2\/categories?post=165"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.waikato.ac.nz\/physicsstop\/wp-json\/wp\/v2\/tags?post=165"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}