Global Warming and the Atmospheric Greenhouse Effect

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" colspan=2 height=90 BGCOLOR="#006699" TEXT="#080000" background="234d05a3.jpg"> <div> <FONT SIZE="5" COLOR="#000000" FACE="Arial" ><B>Arctic Climate Change</B></FONT><B>    </B><B> |    </B><A HREF="id2.htm" TARGET="_top" TITLE="Introduction"><U><B>Introduction</B></U></A></div> <div> <B>Global Warming and the Atmospheric Greenhouse Effect</B>   |   <A HREF="id30.htm" TARGET="_top" TITLE="Temperature Measurements from Earth"><U>Temperature Measurements from Earth</U></A>   |   <A HREF="id55.htm" TARGET="_top" TITLE="Temperature Measurements from Space"><U>Temperature Measurements from Space</U></A></div> <div> </div> </td> </tr><tr> <td valign="top" width=210 BGCOLOR="#FFCC66" TEXT="#080000" background="235d2123.jpg"> <div> <I><IMG SRC="24db4a20.jpg" border=0 width="180" height="162" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></I></div> <bR> <DIV ALIGN="LEFT"></DIV> <div> <I><IMG SRC="24fb4780.jpg" border=0 width="180" height="120" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></I></div> <bR> <div> <I><IMG SRC="278b4c30.jpg" border=0 width="180" height="195" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></I></div> </td> <td valign="top" height=390 BGCOLOR="#FFFFFF" TEXT="#080000"> <div> <I>Global Warming and the Atmospheric Greenhouse Effect</I></div> <bR> <div> <U>The Atmospheric Greenhouse Effect.</U> <FONT SIZE="5" COLOR="#000000" FACE="Arial" > A greenhouse (for plants) is a structure with its walls and roof made of glass.  </FONT></div> <bR> <DIV ALIGN="LEFT"></DIV> <div> <B><IMG SRC="24b902c0.jpg" border=0 width="400" height="300" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></B></div> <div> A common greenhouse.</div> <bR> <div> Glass is used for the roof and walls because it lets sunlight pass through.  The sunlight, which is actually a type of energy called <I><B>solar radiation</B></I>, heats up the plants inside the greenhouse.  The air in contact with the warm plants also becomes warm and begins to rise - this process is called <I><B>convection</B></I>.  The glass walls and roof, because they are solid materials, prevent the rising warm air from leaving the greenhouse.  Since the warm air is trapped, the air inside the greenhouse remains warm.</div> <bR> <div> The atmosphere works in a similar way.  Solar radiation passes through the atmosphere much like sunlight passing through a greenhouse roof, and warms the earth's surface.  Like the sun, which constantly sends out energy in the form of radiation, the earth's surface also sends out a form of energy called <I><B>infrared radiation</B></I>.   The infrared radiation causes certain atmospheric gases, especially <I><B>water vapor</B></I> and <I><B>carbon dioxide</B></I>, to heat up.  Just like the sun and the earth, the warmed-up gases also send out radiation energy.  The radiation from the atmosphere moves in all directions, including downward toward the earth.  The end result is that the atmosphere recycles some of the earth's outgoing infrared radiation, keeping the earth warmer than if there were no atmosphere above it.  </div> <bR> <div> <U>Greenhouse Gases and Global Warming.</U> <FONT SIZE="5" COLOR="#000000" FACE="Arial" > The atmospheric gases that are most responsible for the greenhouse effect are water vapor and carbon dioxide.  However there are others, including methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride.  </FONT></div> <bR> <div> The amounts of certain greenhouse gases, including carbon dioxide, have increased during the past century.  The graph below shows carbon dioxide levels measured in Hawaii since 1958, clearly showing an increase.</div> <bR> <div> <IMG SRC="2501d3e0.jpg" border=0 width="797" height="574" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <div> Atmospheric carbon dioxide levels measured in Hawaii.  The graph shows a clear increase since 1958.  The graph also shows an annual cycle in atmospheric carbon dioxide, a result of photosynthesis (lower concentrations during summer, when photosynthesis is most active, and higher concentrations during winter).</div> <bR> <div> The increase in atmospheric carbon dioxide (CO<FONT SIZE="3" COLOR="#000000" FACE="Arial" >2</FONT>) is mainly due to the burning of fossil fuels: oil, coal and natural gas.  Cutting down trees also contributes to increases in atmospheric carbon dioxide.  Through photosynthesis, trees remove CO<FONT SIZE="3" COLOR="#000000" FACE="Arial" >2</FONT> from the atmosphere.  When a tree is cut down, it can no longer remove CO<FONT SIZE="3" COLOR="#000000" FACE="Arial" >2</FONT><FONT SIZE="5" COLOR="#000000" FACE="Arial" > </FONT>from the air.  In addition, the carbon the tree has accumulated throughout its lifetime will eventually be released back into the atmosphere. No matter which way you look at it, the increase in atmospheric CO<FONT SIZE="3" COLOR="#000000" FACE="Arial" >2</FONT> is due, at least in part, to human activities.</div> <bR> <div> At this point we can attempt to make a logical connection between the greenhouse effect, carbon dioxide and global warming:</div> <bR> <div> The greenhouse effect keeps the earth warm</div> <div> and</div> <div> Carbon dioxide is one of the main greenhouse gases</div> <div> and</div> <div> Atmospheric levels of carbon dioxide have been increasing (pollution caused by humans)</div> <div> and</div> <div> Atmospheric temperatures have been increasing (global warming)</div> <div> THEREFORE</div> <div> Human pollution causes global warming.<FONT SIZE="4" COLOR="#000000" FACE="arial" > </FONT><FONT SIZE="5" COLOR="#000000" FACE="arial" > </FONT></div> <bR> <div> Sounds simple, right?  The problem is, this argument may not be correct.  The atmosphere has many complexities that are not accounted for in the simple argument above.  For example:</div> <div> <IMG BORDER="0" SRC="Symb075c00b7016800000000.png" HEIGHT="24" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The increases in carbon dioxide and temperature don't match.  If you compare the CO<FONT SIZE="3" COLOR="#000000" FACE="Arial" >2</FONT> graph above with the global temperature graph on the Introduction page (<A HREF="id2.htm" TARGET="_top" TITLE="Introduction"><U>click here</U></A>), you will see that the increase in global temperature hasn't followed the same pattern as the increase in CO<FONT SIZE="3" COLOR="#000000" FACE="Arial" >2</FONT>?  Could it be that there are other factors involved? </div> <div> <IMG BORDER="0" SRC="Symb075c00b7016800000000.png" HEIGHT="24" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">What about clouds?  An increase in global temperatures should have resulted in more evaporation of water from the ocean surface.  This will create more clouds which should shade and cool the earth.  In this way, wouldn't a stronger greenhouse effect eventually cause global <I>cooling</I>?</div> <div> <IMG BORDER="0" SRC="Symb075c00b7016800000000.png" HEIGHT="24" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">What about natural cycles?  There are many heating and cooling cycles that we are aware of, and there may be more that we don't fully understand.  For example, daytime temperatures are warmer than nighttime temperatures, yet we don't worry each day that global warming is upon us, because we know that the warming will cycle into cooling in about 12 hours.  Another natural cycle is the annual change in temperature.  Yet another, in many parts of the world, is the 3-7 day cycle in temperatures caused by large high and low pressure systems that move through the atmosphere.  There might be longer cycles, like 1000-year of 10,000-year cycles, that we don't fully understand yet.  If this is the case, then maybe our current global warming will reverse itself and become global cooling in a few hundred years.</div> <div> <IMG BORDER="0" SRC="Symb075c00b7016800000000.png" HEIGHT="24" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">What about the ocean?  Like the atmosphere, the ocean has the important job of carrying heat from the tropics to the north and south poles.  The ocean thus plays a large role in controlling the earth's climate, and it's contribution should not be ignored.</div> <bR> <bR> <div> <IMG SRC="2e593670.jpg" border=0 width="147" height="103" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"><IMG SRC="2e685670.jpg" border=0 width="133" height="103" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"><IMG SRC="2e792670.jpg" border=0 width="146" height="103" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"><IMG SRC="2e844670.jpg" border=0 width="68" height="103" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <bR> </td> </tr></table></body>