A GreaseMonkey script that uses AMEE to add carbon emissions to car journeys in Google Maps (click "raw" to install if you have GreaseMonkey, and then edit to put in your AMEE key details)

google_maps_carbon.user.js

// ==UserScript==
// @name           Google Maps Carbon
// @namespace      http://www.amee.com
// @include        http://maps.google.*/
// ==/UserScript==

// Created by James Smith, AMEE - help@amee.cc
// Public domain, do what you like :)

// Once you've installed the greasemonkey script (click "raw" on the top
// right of the gist to do so), you will need to edit it to set the following
// variables correctly:

server = "stage.amee.com"
username = "your_amee_username_here"
password = "your_amee_password_here"
profile_uid = "your_amee_profile_uid_here"

var Base64 = {
	// private property
	_keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
	// public method for encoding
	encode : function (input) {
		var output = "";
		var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
		var i = 0;
		input = Base64._utf8_encode(input);
		while (i < input.length) {
			chr1 = input.charCodeAt(i++);
			chr2 = input.charCodeAt(i++);
			chr3 = input.charCodeAt(i++); 
			enc1 = chr1 >> 2;
			enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
			enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
			enc4 = chr3 & 63;
			if (isNaN(chr2)) {
				enc3 = enc4 = 64;
			} else if (isNaN(chr3)) {
				enc4 = 64;
			} 
			output = output +
			this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
			this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);  
		}
		return output;
	},
	// private method for UTF-8 encoding
	_utf8_encode : function (string) {
		string = string.replace(/\r\n/g,"\n");
		var utftext = "";
		for (var n = 0; n < string.length; n++) {
			var c = string.charCodeAt(n);
			if (c < 128) {
				utftext += String.fromCharCode(c);
			}
			else if((c > 127) && (c < 2048)) {
				utftext += String.fromCharCode((c >> 6) | 192);
				utftext += String.fromCharCode((c & 63) | 128);
			}
			else {
				utftext += String.fromCharCode((c >> 12) | 224);
				utftext += String.fromCharCode(((c >> 6) & 63) | 128);
				utftext += String.fromCharCode((c & 63) | 128);
			}
		} 
		return utftext;
	},
}

function directionsLoaded(event) {
  node = event.relatedNode;
  if ((node.className == "altroute_info") && node.textContent.indexOf('(') == -1) {
    addCO2Value(node);
  }
  if (node.id == "panel4") {
    infonode = document.getElementById("dditd");
    if (infonode.textContent.indexOf('(') == -1) {
      addCO2Value(infonode);
    }
  }
}

function addCO2Value(node) {
  // Get distance out of content
  str = node.textContent;
  str = str.replace("\xA0"," ");
  var distance = str.split(" ");
  // Get co2 data from AMEE 
  gmAjax({
      method: 'GET',
      url: 'http://'+server+'/data/transport/car/generic/drill?size=average&fuel=average',
      headers: {
          'Accept': 'application/json',
          'Authorization':'Basic '+Base64.encode(username+":"+password)
      },
      onload: function(responseDetails) {
          response = JSON.parse(responseDetails.responseText);
          var itemname = (new Date).getTime();
          uid = response['choices']['choices'][0]['value']
            gmAjax({
              method: 'POST',
              url: ('http://'+server+'/profiles/'+profile_uid+'/transport/car/generic') ,
              headers: {
                  'Accept': 'application/json',
                  'Authorization':'Basic '+Base64.encode(username+":"+password),
                  'Content-type':'application/x-www-form-urlencoded'
              },
              data: 'dataItemUid='+uid+'&distance='+distance[0].replace(',','')+'&representation=full&distanceUnit='+distance[1]+'&name='+itemname,
              onload: function(responseDetails) {
                response = JSON.parse(responseDetails.responseText);
                amount = parseFloat(response['profileItems'][0]['amount']['value'])
                node.textContent += " ("+amount.toString()+" kg CO2e)";
              }
          });
      }
  });
}

element = document.getElementById("opanel4");
element.addEventListener("DOMNodeInserted", directionsLoaded, true);

var ajaxQueue = [];
var processAjaxQueue = function(){
  if (ajaxQueue.length > 0) {
    for (ajax in ajaxQueue) {
      var obj = ajaxQueue[ajax];
      GM_xmlhttpRequest(obj);
    }
    ajaxQueue = [];
  }
}
setInterval(function(){
  processAjaxQueue();
}, 100);

function gmAjax(obj){
  ajaxQueue.push(obj);
}