When talking about climate change, not all fossil fuels are created equal. Burning natural gas, for instance, produces nearly half as much carbon dioxide per unit of energy compared with coal. Natural gas is thus considered by many to be a “bridge fuel” that can help nations lower carbon emissions while they transition more slowly from fossil fuels to renewable, carbon-neutral forms of energy. The recent boom in natural gas production in the United States, for instance, contributed to a 3.8 percent drop in carbon emissions in 2012.
But natural gas has a climate downside—it’s mostly composed of methane. “Methane is a potent greenhouse gas,” said energy researcher Adam Brandt of Stanford University. The gas is about 30 times better at holding in the atmosphere’s heat compared with carbon dioxide. So if enough methane leaks during production, natural gas’s slim advantage over other fuels could be wiped out.
A report published today in Science, however, concludes that the United States’ leaky natural gas production system currently isn’t leaking enough methane to make it worse fuel for the climate than coal.
The natural gas production system is not sealed tight. There are some areas where methane is allowed to leak intentionally for purposes of safety, but there’s also a lot of leaky valves and cracked pipes out there that can let the gas out. Quantifying all those leaks, though, has proven tricky.
The Environmental Protection Agency provides estimates of methane emitted in the United States. To calculate these estimates, someone has to go to a facility and take direct measurements from various equipment and devices. Those measurements are added up to get a total for the facility. And the facilities where the measurements are taken will serve as the basis for calculations of methane emissions for a type of source or a region.
These official estimates, however, probably underestimate total methane leaked because the devices that are sampled to provide those estimates aren't necessarily representative of all of the devices used by the natural gas industry to produce and move its product. In addition, sampling is expensive and limited. It also only takes place at locations where facilities let the EPA in—those facilities may be different from the average facility, leading to sampling bias.
Studies that have directly measured methane levels have gotten much different results. Atmospheric tests that have covered the entire United States come up with methane emissions that are about 50 percent higher than the EPA estimates, according the new paper in Science. Partly that’s because air sampling will pick up both anthropogenic methane and methane from natural sources, such as wetlands. But it’s also because the EPA’s methods are so inaccurate—natural sources only account for a fraction of the discrepancy.
The air sampling studies, though, have found some odd peaks in regional methane emissions, causing scientists to worry that there could be a lot more methane leaking from sites of natural gas production than thought. So Brandt and his colleagues began tallying up all the places where natural gas production could be leaking methane along with other sources of methane that could be mistaken for natural gas emissions.
The large natural gas leaks suggested in regional studies “are unlikely to be representative of the entire [natural gas] industry,” they write. If there were natural gas leaks of that magnitude across the natural gas industry, then methane levels in the atmosphere would be much higher that surveyed in the air sampling studies. “Most devices do not leak,” Brandt noted. Only about 1 to 2 percent of the devices used in natural gas production leak any methane, and large emitters—what the researchers nickname “superemitters”—are even rarer.
Brandt and his team then took a look at all the excess methane being released into the atmosphere. For their calculations, they assumed all that methane was coming from the natural gas industry. That’s unlikely, they note, but it makes for a good worst-case scenario. But even that level of methane wasn’t enough to make natural gas a bigger greenhouse gas contributor than coal, the researchers found. And switching from coal to natural gas for energy production does reduce the total greenhouse effect on a scale of 100 years, the standard scientists use in calculations like these.
“We believe the leakage rates are likely higher than official estimates, but they are unlikely to be high enough to disfavor shifting from coal to natural gas,” Brandt said.
Natural gas has also been promoted as a cleaner fuel than diesel, and it’s replaced that fuel in many trucks and buses on city streets. But the climate benefits of such a switch are not as clear as the switch from coal to natural gas.
Taking into account methane leaks from extraction all the way down the pipeline to the pump may actually make natural gas less climate friendly than diesel. But it’s probably not time to abandon the natural gas bus. “There’s all sorts of reasons we might want to [replace] diesel buses,” Brandt says. For example, burning natural gas results in less air pollution and less reliance on imported petroleum.
For natural gas to assert itself as a more environmentally friendly fuel, though, the industry is going to have to plug up its leaky system. Companies may find it worth their while to do so, and not simply for the climate benefits. Less leakage equals more profit, and plugging just a few of the biggest leaks could easily increase income, Brandt says. “If we can develop ways to quickly and cheaply find these sources, it’s going to be very profitable for companies.”
Tunapozungumzia mabadiliko ya hali ya hewa, si mafuta yote ya visukuku yaliyoundwa sawa. Kwa mfano, kuchoma gesi ya asili hutokeza karibu nusu ya kaboni dioksidi kwa kila kitengo cha nishati ikilinganishwa na makaa ya mawe. Gesi ya asili ni hivyo kuchukuliwa na wengi kuwa 'bridge mafuta' ambayo inaweza kusaidia mataifa kupunguza uzalishaji wa kaboni wakati wao mabadiliko polepole zaidi kutoka mafuta ya makaa ya mawe kwa mbadala, kaboni-neutral aina ya nishati. Kwa mfano, ongezeko la hivi karibuni la uzalishaji wa gesi ya asili nchini Marekani, lilisaidia kupunguza uzalishaji wa kaboni ya kaboni kwa asilimia 3.8 mwaka 2012. Lakini gesi ya asili ina hali ya hewa chini - ni hasa linaundwa na methane. "Methani ni gesi yenye nguvu ya chafu", akasema mtafiti wa nishati Adam Brandt wa Chuo Kikuu cha Stanford. Gesi hiyo ina uwezo wa kuhifadhi joto mara 30 zaidi ikilinganishwa na kaboni dioksidi. Kwa hiyo ikiwa methani ya kutosha itatoka wakati wa uzalishaji, faida ndogo ya gesi ya asili juu ya mafuta mengine inaweza kuharibiwa. Ripoti iliyochapishwa leo katika Sayansi, hata hivyo, inahitimisha kwamba mfumo wa uzalishaji wa gesi asilia wa Marekani kwa sasa hautoi methane ya kutosha kuifanya kuwa mafuta mabaya zaidi kwa hali ya hewa kuliko makaa ya mawe. Mfumo wa uzalishaji wa gesi asilia haujahifadhiwa vizuri. Kuna baadhi ya maeneo ambapo methane inaruhusiwa kuvuja makusudi kwa madhumuni ya usalama, lakini pia kuna mengi ya valves leaky na mabomba cracked huko nje ambayo inaweza kuruhusu gesi nje. Hata hivyo, imethibitika kuwa vigumu kujua kiasi cha uvujaji huo wote. Shirika la Ulinzi wa Mazingira hutoa makadirio ya methani inayotolewa nchini Marekani. Ili kuhesabu makadirio haya, mtu lazima aende kwenye kituo na kuchukua vipimo vya moja kwa moja kutoka kwa vifaa na vifaa mbalimbali. Vipimo hivyo huongezwa ili kupata jumla ya kituo hicho. Vifaa vya kupima na kupima metani vinaweza kutumika kama msingi wa hesabu ya uzalishaji wa metani kwa aina fulani ya chanzo au mkoa. Hata hivyo, makadirio haya ya rasmi yaweza kupunguza jumla ya methane iliyopatikana kwa sababu vifaa vilivyochukuliwa kutoa makadirio hayo sio lazima kuwakilisha vifaa vyote vinavyotumiwa na tasnia ya gesi ya asili kuzalisha na kusafirisha bidhaa zake. Kwa kuongezea, kuchukua sampuli ni ghali na ni ndogo. Pia hufanyika tu katika maeneo ambapo vifaa kuruhusu EPA katika-hizi vifaa inaweza kuwa tofauti na kituo cha wastani, na kusababisha sampuli bias. Uchunguzi uliopima moja kwa moja viwango vya metani umepata matokeo tofauti sana. Uchunguzi wa hali ya hewa uliofanyika nchini Marekani ulionyesha kuwa uzalishaji wa gesi ya methane ni wa asilimia 50 zaidi ya makadirio ya shirika la ulinzi wa mazingira (EPA). Kwa sehemu hiyo ni kwa sababu sampuli ya hewa itachukua methane ya anthropogenic na methane kutoka vyanzo vya asili, kama vile maeneo ya mvua. Lakini pia ni kwa sababu mbinu za EPA ni zisizo sahihi sana vyanzo vya asili huelezea sehemu ndogo tu ya kutofautiana. Uchunguzi wa sampuli za hewa, hata hivyo, umegundua kilele cha gesi ya methani katika maeneo ya mkoa, na kusababisha wanasayansi kuwa na wasiwasi kwamba kunaweza kuwa na methani zaidi ya kuvuja kutoka kwa maeneo ya uzalishaji wa gesi ya asili kuliko walivyofikiri. Brandt na wenzake walianza kuhesabu maeneo yote ambapo uzalishaji wa gesi asilia unaweza kuwa na methane pamoja na vyanzo vingine vya methane ambavyo vinaweza kuwa na makosa kwa uzalishaji wa gesi asilia. Uvujaji mkubwa wa gesi asilia uliopendekezwa katika masomo ya kikanda "hauna uwezekano wa kuwa mwakilishi wa tasnia nzima ya [gesi asilia]," wanaandika. Ikiwa kuna uvujaji wa gesi ya asili ya ukubwa huo katika sekta ya gesi ya asili, basi viwango vya methane katika anga itakuwa juu zaidi kuliko uchunguzi katika masomo ya sampuli ya hewa. "Vifaa vingi havivuji", Brandt alisema. "Hata hivyo, ni asilimia moja hadi mbili tu ya vifaa vinavyotumiwa katika uzalishaji wa gesi ya asili vinavyotoa gesi ya methani, na vyombo vikubwa vinavyotoa gesi ya methani, ambavyo watafiti wanaviita ""superemitters,"" ni nadra zaidi." Kisha Brandt na kikundi chake wakachunguza kiasi kikubwa cha metani kilichokuwa kikitolewa angani. Kwa ajili ya mahesabu yao, walidhani kwamba metani yote hiyo ilitoka katika sekta ya gesi asilia. Wao wanasema kwamba hilo haliwezekani, lakini hilo linaonyesha hali mbaya zaidi. Lakini hata kiwango hicho cha methani hakikutosha kufanya gesi ya asili iwe mchangiaji mkubwa wa gesi ya chafu kuliko makaa ya mawe, watafiti waligundua. "Kubadilisha makaa ya mawe kwa gesi ya asili kwa ajili ya uzalishaji wa nishati hupunguza athari ya jumla ya chafu kwa kiwango cha miaka 100, ""alisema." "Tunaamini viwango vya uvujaji vinaweza kuwa vya juu kuliko makadirio rasmi, lakini haiwezekani kuwa vya juu vya kutosha kupinga mabadiliko kutoka makaa ya mawe hadi gesi asilia", Brandt alisema. Gesi ya asili pia imekuzwa kama mafuta safi kuliko dizeli, na imebadilisha mafuta hayo katika malori na mabasi mengi barabarani jijini. Lakini faida za hali ya hewa za kubadili kama hiyo si wazi kama kubadili kutoka makaa ya mawe hadi gesi asilia. Kwa kuzingatia uvujaji wa methane kutoka kwa uchimbaji hadi kwenye bomba, inaweza kufanya gesi ya asili iwe na uaminifu wa hali ya hewa kuliko dizeli. Lakini labda si wakati wa kuacha basi la gesi ya asili. "Kuna sababu nyingi sana ambazo huenda tukataka [kubadilisha] mabasi ya dizeli", anasema Brandt. Kwa mfano, kuchoma gesi ya asili husababisha uchafuzi wa hewa mdogo na utegemezi mdogo kwa mafuta ya nje. Hata hivyo, ili gesi ya asili iweze kujitangaza kuwa mafuta yenye kuhifadhi mazingira, sekta hiyo itahitaji kufunga mfumo wake unaopunguka. Kampuni zinaweza kupata ni thamani yao wakati wa kufanya hivyo, na si tu kwa ajili ya faida ya hali ya hewa. "Kupunguza uvujaji wa maji ni sawa na faida zaidi, na kuziba tu chache za uvujaji mkubwa inaweza kwa urahisi kuongeza mapato, ""Brandt anasema." "Ikiwa tunaweza kuendeleza njia za haraka na nafuu kupata vyanzo hivi, itakuwa ni faida sana kwa makampuni. "