I need to get down to Christchurch to visit some friends. It has simply been too long and they are going to forget I exist. I was already to hop into my trusty rusty old Subaru when Marg caught me up. “What about your emissions? How much greenhouse gas are you going to produce? You know, we all need to do our bit.”
Crikey! I hadn’t thought about that! It was time to put pencil to paper and resurrect the maths I learned back in the Pleistocene (i.e., how many woolly mammoths does it take to…). Let’s see…
The Subaru uses 10 litres petrol per 100 km and a litre of petrol produces 2.4 kg of CO2. Google Maps tells me that the round trip from Blenheim along Hwy 1 is 614 km. So, if I drive, I’ll produce 147 kg of CO2. That is close to twice my weight in greenhouse gas! Is there a better option?
Air New Zealand calculates your emissions when you book flights, so a quick play on the internet finds that I’ll produce 69 kg CO2 for the 490 km round trip. That’s better, and the flight is a bit of fun if the weather is clear (and a bit of terror if it is not). Now it is down to under my weight in CO2, at least.
But I haven’t taken the train since the tracks were reopened after the earthquake. How about that? Kiwirail is a bit cagey about their emissions per passenger-kilometre, so I turn to the trusty Department of Environment, Food and Rural Affairs (DRFRA) tables from the UK. These are tables that businesses use to calculate their emissions, as required by law in the UK. Here I find that the round trip would produce about 27 kg CO2. Better still! About a third my weight in CO2. And I get to brag about how beautiful the Coastal Pacific trip is to my mates who haven’t ridden it yet.
I’m all ready to book the ticket when Marg appears again, like the little voice in my conscience, whispering into my ear. “What about the bus?” Nuts. Do I really want to take the bus? Granted, it would be the cheapest option. “OK, I’ll check”, I growl. Out come the DRFRA tables again and it’s only 17 kg CO2 for the round trip! That’s about one-eighth of what it would be if I took the Subaru!
Marg smiles. “So, you’ll be taking the bus, right? And you can ride your bicycle to the bus station with your backpack! My handsome eco-warrior.” She has me. Looks like I’ll be taking the bus.
I am in support of the student strike for climate action, coming up next Friday, and here’s why: I’m reminded of my own days of student strikes, nearly 50 years ago, in a big powerful country across the Pacific. I was a freshman in engineering, newly settled in student dorms, loyally following in my father’s footsteps. And the madness of Vietnam War was raging on. My older brother had been drafted and was in the thick of it – walking point in the jungle and hoping not to kill anyone and make it out in one piece. My draft lottery number was 40; I would be an early pick by the draft board when my student deferment ran out. The university was on strike. There were student protests nearly every day and police curfews at night. A bank was burned to the ground. A student was killed by a police bullet. Hundreds of students were arrested. Then, as now, the grownups asked, “Do these silly kids think they can really change anything?” “They should stay in class and learn something about the world before they protest!”
And we were right. We now know fully well that war was a cruel, cynical and worthless waste of blood and treasure. We students didn’t know all the history or whether to believe the “domino theory” of communist aggression in Southeast Asia. We didn’t know that our political leaders were lying to us about the progress of the war and the magnitude of civilian casualties. We just knew something was inherently wrong with invading another country and killing its people to win their “hearts and minds” and keep them from joining a rival political alliance. There was something in our nation’s founding documents, things we learned in grammar school, that said this wasn’t right.
The arguments with my father were epic. He had too much invested in keeping the status quo – the job in the defense industry, the mortgage, the family, the retirement – to want to rock the boat. It was easier and simpler to believe the president and carry on. His conscience was clouded by the daily responsibilities of life. We had none of these entanglements. We had ideals and energy, and our consciences were free to honour those ideals. We thought a lot about the future and how it could be better.
I would like to think that our protests helped end the Vietnam War. In any event, it was the right thing to do. What would our political system be like if a few courageous colonists hadn’t stood up to mad King George and devised a new system of governance that didn’t need kings? What would our labour laws look like without the sacrifices of striking workers of two centuries ago, trampled under the hooves of mounted police? Sometimes, when change is needed, we need to protest. It isn’t always easy and without sacrifice. Many have paid with nightstick lumps on the head, with days in court and nights in jail… and some with their very lives. With the benefit of history, we now call these people heroes. Their sacrifice is the dues that we periodically need to pay to live in a free and just society.
So, as the world charges headlong into future of climate instability, I can understand those who react like my father: “Give stability and prosperity to me and my family and don’t rock the boat!” For young people, like I was so many years ago, it is different. They are all potential with little to lose, brimming with passion, ideals, and newly acquired knowledge about our world. I said, “Give me a future without war!” Today, they simply say, “Give me a future!”
If New Zealand is to achieve zero net greenhouse gas emissions by 2050, we will all need to cut these emissions in our daily lives. That means changing our lifestyles to low greenhouse gas alternatives. We know about the greenhouse gas emissions from burning fossil fuel – the principal contributor to global warming worldwide. But there are also substantial emissions associated with many of the foods we eat. And, unfortunately, the highest emissions are associated with some Kiwi favourites – beef, lamb and venison.
Ruminants, the group of animals including cattle, sheep, goats and deer, have chambered stomachs which allow them, with the help of bacteria, to digest the cellulose fibre in grass and hay. Unfortunately, some of these bacteria also generate methane gas, a potent greenhouse gas, which gets released to the atmosphere. In addition, pasture fertiliser and cattle urine are rich in nitrates, part of which are converted by soil bacteria to nitrous oxide gas, another potent greenhouse gas. Methane and nitrous oxide emissions are largely responsible for pushing red meat up in the emissions ranking.
According to a 2011 report by Environmental Working Group, a US non-profit advocating for consumer product safety and sustainability, a kilogram of consumed beef – the beef we actually eat - produces the equivalent of 27 kilograms of CO2 from burned fossil fuels. The shorthand for this is 27 kg of “CO2e” (carbon dioxide equivalents), to account for greenhouse gases other than CO2. So what does 27 kg mean in this context? For comparison, a kilogram of consumed beef creates about the same amount of greenhouse gas as a drive from Blenheim to Nelson and back in a standard petrol passenger car.
Keep in mind that the value for New Zealand beef, which is mostly grass-fed, may be different than that for US beef, which is largely grain-fed. But while there are emissions associated with feed grain, that are not associated with grass-fed beef, these emissions could be more than offset by the slower growth rate of our grass-fed beef (meaning more lifetime emissions), so the exact difference is unclear. The other important point about this ‘emissions value’ of 27kg is that it includes production, transportation, processing, cooking and waste!
Lamb is even higher, at 39 kg CO2e per kg of meat consumed, largely because less of the animal is used for food. Pork, chicken and eggs produce less of these emissions, at 12.1, 6.9 and 4.8 kg CO2e per kg, respectively, and may be better meat choices for the climate-conscious consumer.
So, if cattle produce so much greenhouse gas, what about dairy products which come from cattle? Cheese tops the scale of non-meat foods, with 13.5 kg CO2e per kg consumed; more than pork. The emissions associated with air freighted imported cheese are about 46% higher, so it is far better to eat New Zealand cheese. By comparison, yogurt and tofu each produce about 2 kg CO2e per kg consumed (as long as they are not being flown into the country!).
Milk is relatively low, at 1.9 kg CO2e per kg consumed, but Kiwi consumers tend to drink quite a bit of it, so the emissions add up. The emissions from milk substitutes, such as soy, pea or almond milk, are quoted from a number of sources and are around 0.4 kg CO2e per kg. The value for milk substitute actually consumed will be slightly more, to include waste and transport, but will still be about a quarter of that of cow’s milk.
The emissions associated with fresh vegetables are relatively low; for example, 2.0 kg CO2e per kg consumed for broccoli and 1.1 for fresh tomatoes. Interestingly, about a quarter of the emissions associated with these fresh vegetables is due to waste and another quarter due to transport. This shows the importance of buying locally grown produce in keeping emissions low. Air freighting fruit and vegetables from California generates another 1.2 kg CO2e per kg. Sea freighting that same distance generates only an additional 0.2 kg CO2e per kg.
Grains and beans have relatively low emissions. Rice ranks highest at 2.9 kg CO2e per kg consumed due to methane produced in waterlogged rice paddies. Lentils rank lowest with 0.9 kg CO2e per kg consumed, half of which is due to the energy needed to cook them.
Learning about these values has certainly changed my eating habits and, hopefully, these values will also have you thinking about how to reduce your household’s emissions. Food for thought, if nothing else!
Greenhouse gas emissions (GHGs) will need to be cut back if the worst of global warming is to be avoided. So, how much GHG do we produce in our daily lives? Where can we make cuts on these emissions?
Here are some general numbers which may help us in our daily decisions. Let’s start with transportation and consider the trip from Blenheim to Christchurch and back, a distance of about 614 km on Hwy 1. One litre of petrol produces about 2.4 kg of CO2 when burned in an automobile. So, if your car uses 10 litres fuel per 100 km, each 100 km trip produces about 24 kg of CO2. Every 50 litre tank of petrol creates 120 kg of CO2. Diesel fuel produces slightly more, or about 2.7 kg CO2 per litre. So, in a vehicle using 10 litres of petrol per 100 km, would create about 147 kg of CO2.
But what if we decide to fly instead? Air New Zealand’s carbon offset calculator shows a flight to Christchurch and back to be 490 km and a single passenger produces 69 kg CO2, just under half the amount from driving. With respect to emissions, it is better to fly to Christchurch and back than it is to drive, unless you have two or more persons in the car or your car gets double the fuel efficiency (i.e., 5 litres per 100 km).
And then there are the emissions from food to consider. Information from USA has calculated the emissions in CO2e (CO2 equivalents, to account for other greenhouse gases, as well as CO2) per kilogram of consumed product. Keep in mind though that these numbers include processing, transport, cooking, wastage and disposal. Lamb tops the list, with 39 kg CO2e per kg consumed meat. Beef is somewhat lower at 27 kg per kg consumed. Mind you, these are US numbers, where beef and lamb are largely grain fed. Nearly 5 kg CO2e per kg consumed beef is due to feed production, which would be much less here, where most beef is grass fed. The emissions from lamb are higher than beef because less of the animal is used for food.
These numbers show that it doesn’t take many barbeques to match the emissions of a road trip to Christchurch and back. This example illustrates that cutting back on beef and lamb may go a long way to cutting a family’s greenhouse gas emissions. Pork (12 kg CO2e/kg consumed), chicken (7 kg CO2e/kg consumed) and eggs (5 kg CO2e/kg consumed) are lower emissions alternatives.
Cheese tops the dairy category, at 13.5 kg CO2e/kg consumed, with milk and yoghurt each around 2 kg CO2e/kg consumed. Surprisingly, most vegetables, nuts and legumes range from 3 kg CO2e/kg consumed (potatoes & rice) to 1 kg CO2e/kg consumed (tomatoes & lentils), largely due to wastage of fresh vegetables or the energy needed to cook potatoes, beans and lentils. A simple pressure cooker to cook beans and lentils will decrease emissions by decreasing cooking time. Propane for your hob produces around 3 kg CO2 per kg burned.
And of course, buying local can reduce the transport costs. A kg of fresh fruit airfreighted from California creates another 1.2 kg CO2e emissions.
What about waste? All organic material decomposes to CO2 and methane in municipal landfills, creating emissions. This includes paper (1042 kg CO2e/tonne), wood (828 kg CO2e/tonne) and mixed food & garden waste (587 kg CO2e/tonne). Composting can reduce the emissions from food scraps and garden waste by roughly 50%. We in Marlborough are lucky because the council flares (burns) the gas emitted by the Bluegums landfill, significantly reducing these emissions.
Hopefully, these values will have you thinking about how you could decrease your household’s emissions.
 The Environmental Working Group
At the Earth Day Party last April at A&P showgrounds, Richard and Madison queried, “The problem of climate change is overwhelming. What simple things can I do to make a difference?”
There are many sources of advice on how to cut greenhouse gas emissions and prepare for the changing climate ahead. Climate Karanga Marlborough suggests these to be the top seven for people living on the top of the South Island:
1. Try to cut your fossil fuel consumption. According to the latest Ministry for the Environment (MfE) inventory, carbon dioxide emissions from transportation and energy (electricity generation) made up 40% of New Zealand’s emissions in 2016. Electricity here on the South Island is almost entirely renewable, so electric power here creates minimal emissions. In order to cut fuel use, try driving less and carpooling if you can. If you haven’t used it, get to know your local public transport systems; it may be a good alternative to taking the car. Consider riding a push bike or an e-bike for local trips; it’s good for your health, saves emissions and it’s fun! Consider an electric car if your commute is suitable; and you will save significantly on fuel.
2. If you do need to drive a petrol car and fly, consider purchasing carbon offsets. These are certified programs in which you can purchase carbon dioxide uptake in forestry or other emissions saving projects to offset your emissions. Air New Zealand offers offsets for its flights. EKOS in Takaka and Enviro-mark Solutions of the US offer carbon offsets for a wide range of emissions.
3. Buy local goods and produce. Needless to say, there are fairly large emissions associated with international air and sea shipping. Buying local also helps your local economy.
4. Cut back on meat and dairy. It is an unfortunate fact for New Zealand that cattle, sheep and deer create methane in their digestive systems, which is a much more intense greenhouse gas than carbon dioxide. Fertiliser application and urine from cattle also create nitrous oxide emissions, which are an even more intense than methane and also help to destroy the ozone layer, increasing the risk of sunburn and skin cancer. According to the MfE, agriculture accounted for 49% of New Zealand’s emissions in 2016. While ongoing scientific research is looking for ways to reduce emissions from farming, cutting back on meat and dairy is a quick way to accomplish this in the meantime.
5. Look for opportunities to sequester (capture and store) carbon dioxide on your land and in your community. These might include tree planting and preservation, and farming practices designed to sequester carbon dioxide in soils, such as “regenerative” farming.
6. Get active. Encourage local councils, businesses, friends and relatives to cut emissions. Submit on the local and national government’s climate change action plans and legislation. There is only so much individuals can do in their personal lives to limit emissions. In order to be fair and effective, action to address climate change will need to be a coordinated and spread throughout our economy, in a national effort.
7. Participate in community preparedness. With wild weather expected in the years ahead, we’ll all need to know our neighbours and be ready when disaster strikes. New Zealanders are already pretty good at this already, thanks to earthquakes, but we’ll need to up our game. I was in Santa Rosa, California, during the firestorms of October 2017 that destroyed 5,300 homes. Neighbours knocking on doors in the middle of the night saved many lives.
One further recommendation is to calculate your family’s carbon footprint. The MfE website has a link to an ecological footprint calculator hosted by Global Footprint Network. Go to: “We all have a role to play”/”What you can do”. Unfortunately, the calculator doesn’t give you a breakdown of your individual emissions sources but you can discover this by running separate test cases (e.g., setting all activities to zero while testing one activity, such as air travel). Enviro-Mark Solutions offers a calculator with which you can purchase offsets.
Climate change is creating a double whammy on the farming industry in New Zealand. On one hand, farmers will bear most of the brunt of extreme weather that is on the way. How many of us are likely to see our livelihoods literally drown in floods, roasted in heat waves, starved in droughts, fried in wildfires or blown down in cyclones? This is what scientists predict, and looking at their predictions going back to the 1980s, they’ve been close to spot on, if not perhaps a bit conservative.
On the other hand, farmers are being asked to join the New Zealand emissions trading scheme (ETS) and account for the greenhouse gases methane and nitrous oxide emitted by agriculture. Methane being from the digestive systems of livestock and nitrous oxide principally from animal waste. Including these gases in the ETS would require farmers to either reduce these emissions in the coming years or buy carbon credits to cover their emissions above a certain threshold, with that threshold scheduled to gradually decline from year to year. At best, farmers will have to adapt to new ways of farming and at worst, farming is going to get more expensive relative to competitors overseas who don’t take steps to limit their emissions. Either way, the farmer’s life is going to get tougher.
The national debate on including methane and nitrous oxide in the ETS and in New Zealand’s zero emissions targets will require tough choices and clear-eyed discussion. Articles like the recent opinion editorial by Stuart Smith in this newspaper (“Emission impossible: Cars, not cows, the real threat to climate”, 3 November 2018) do not help. Attempts to shift the blame from agriculture to transport for GHG emissions only hardens opposing positions and delays effective decision making, delays that humanity can ill-afford at this point.
Here are some facts that need to be considered in this debate:
It is argued that methane is a short-lived pollutant and therefore should be treated differently. But, “short-lived” is relative. Methane stays in the atmosphere for an average of 9 years, which, according to the latest IPCC report, is about the time frame humanity has to stabilise greenhouse gas (GHG) emissions in order to avoid the worst impacts of global climate change. And methane is a much more potent greenhouse gas than CO2, producing 104 times the global warming potential (GWP) of an equivalent weight of CO2 over a 20 year period. Even over CO2’s average 100 year lifetime in the atmosphere, methane yields 25-32 times the GWP of CO2. Nitrous oxide is worse still, creating 298 times the GWP of CO2 over a 100 year period, as well as causing depletion of stratospheric ozone, leading to more sun burns and skin cancer. In short, methane and nitrous oxide are much worse greenhouse gases than CO2, especially when we consider the speed with which we need to act. CO2 is only the most damaging greenhouse gas emission because there is so much more of it emitted worldwide.
New Zealand is unique in producing a relatively high proportion of methane and nitrous oxide compared to other countries. In fact, we have the highest per capita emissions of these gases worldwide. The Ministry for the Environment website lists agriculture as the source of 49% of New Zealand’s GHG emissions in 2016, compared to 40% from energy and road transport. This analysis equates the GWP of methane and nitrous oxide to that of CO2 over a 100 year time frame. If we consider the effects of methane emissions over a shorter time frame, say over the next 20 years, our methane emissions will have several times the warming impact of our CO2 emissions and easily create the lion’s share of our nation’s contribution to global warming today.
I empathise with those who wish to shield agriculture from the economic cost of limiting GHG emissions. But it makes no sense to penalise one industry over another for their respective contributions to a global problem. The best we can do is to help New Zealand agriculture shift to low GHG farming techniques and support the farming science community in pioneering new ways to limit emissions. We, as a nation, will also need to help NZ agriculture adjust to the severe and unpredictable weather expected to come with continued global warming, which we already see impacting farming overseas. Of all the sectors of our economy and communities, agriculture will be the hardest hit by the changes expected to come.
At the Marlborough Earth Day party, held at A & P showgrounds in April, a number of visitors were asked if there were aspects of climate change that they wondered about. Amelia asked, “Is there a reliable, neutral source of information; information I can trust?”
Like Amelia, many of us grapple with this question. Most of us get our information about climate change from the news. Here it is important to remember that news is a business. Success is measured by how many sets of eyes see the pages they print, so there is always the incentive to sensationalise news stories. Of course, getting news stories wrong can lead to corrections and a loss of readership so the urge to sensationalise news has natural limits.
On the other hand, climate science is complex so news about climate science is more often than not a gross simplification of what the scientist actually says, and its ramifications to our future. Therefore, although I believe the great majority of science journalists are earnest in their attempts to convey climate science, it is a task prone to oversimplification and sensationalism. At best, news articles on climate science should be read with a skeptical eye, and at worst double checked with other information.
So what about the science sources themselves? On the whole the information is more reliable but with certain precautions. Here we need to consider the business aspects again. Most science is paid for by governments, private institutions and industry for obvious reasons; science is the primary driver of progress in technology, medicine and understanding that have combined to improve all of our lives in the last few centuries.
Most of the time, the sponsors of science welcome its results. Sometimes, however, and particularly when it comes to the environment, science tells industry something it doesn’t want to hear. In the case of climate science, the central findings that mankind needs to stop burning fossil fuel, stop cutting down indigenous forests and change agricultural practices presents a serious threat to many established businesses. There have been a number of times in recent history when this has happened on other environmental issues, such as with acid rain and atmospheric ozone depletion, and we know that the common initial response of threatened industry is to fight back with information campaigns challenging the certainty and consensus of the scientific community. While we see many threatened companies embracing the science and acting to reduce emissions, we still see a chorus of industry sponsored “experts” attempting to portray controversy and uncertainty in the science when none actually exists. The American Geophysical Union, the world’s largest organisation of earth, ocean and atmospheric scientists, has had a position statement laying out the threat of human-caused climate change since 1998.
There are a few strategies that one can adopt in wading through the literature on climate change. For background information about climate change, government scientific agency websites (such as NIWA in NZ and NOAA in the US) are good sources of accurate and simplified information but are somewhat regionally specific. NASA, the US space administration, has an excellent website with news, latest research and impressive graphics and photographs.
When reading mainstream news articles on the latest developments in climate science, it can help to follow links to the author’s website or search it separately. The academic articles you will be directed to might be a bit heavy on scientific jargon, however. Carbon Brief is a UK website devoted to climate news (www.carbonbrief.org) with many academic scientists as contributing editors, which strives to simplify and explain the science and do fact checks on other climate news. Another very good site is Skeptical Science (https://www.skepticalscience.com/). This site has a range of information from climate scientists and has an excellent section where you can read responses to various climate change myths.
In conclusion, reliable information is out there but for some sources it takes reading with a skeptical eye as to the motivations of the authors and, at times, double checking. As a general rule, the closer you can get to what climate scientists actually say, the better.
At the Marlborough Earth Day party, held at A & P showgrounds in April, a number of visitors were asked if there were aspects of climate change that they didn’t understand. Liam asked, “How does climate change affect me personally?”
The short answer is, “not much, yet”. While some parts of the world have experienced dramatic warming and weather extremes related to human-caused climate change, New Zealand has largely been spared. We are surrounded by oceans which tend to moderate temperatures on land, and the oceans around us have been warming only gradually. Perhaps the most apparent evidence of climate change that we see is warmer ocean temperatures, drawing us into the water more during summer holidays.
Aside from the planet’s poles, where warmer temperatures are abundantly apparent in melting glaciers and vanishing sea ice, the natural weather cycles in most temperate and tropical countries make rising temperature hard to see in people’s daily lives. Was the last hot day due to climate change or just a natural weather cycle? We’ve always had heat waves. What is different now?
Here we must rely on climate scientists to tease out the long term trends in our constantly changing weather. They’ve observed global temperatures, measured at carefully designed sites around the world, to be increasing. On average, the earth’s surface has warmed by about 1 degree Centigrade since 1950. One degree is not much and would be a challenge for any of us to detect in our lifetimes, but it is a lot when compared to previous temperature variations, from historic records and as determined from ice cores of ancient snowfall.
Another principal threat of climate change, an increasing frequency of extreme weather events, has been predicted by weather computer models and is only now beginning to emerge, in a statistical sense, from the historical record of destructive storms, prolonged droughts and intense heat waves. Here the long term trends are more difficult to discern due to the episodic nature of these events (coming perhaps every few years or decades) and our relatively short history of eyewitness accounts. Add to this the fact that climate model predictions suggest global warming won’t necessarily increase the number of storms, but will increase the intensity of the storms that come. How many destructive storms does it take for scientists to determine a reliable trend toward greater (or lesser) storm intensity? It is a tricky problem, which is why we are only now seeing trends of more extreme weather. Unfortunately, the computer models suggest that weather extremes will only become more common as the planet warms. We may not see it now, but we can expect to in years to come.
So, in considering Liam’s question, although we haven’t experienced much change yet, we can see that changes are coming and they are almost all detrimental to our economy and way of life, and to the natural environment. I’ve mentioned only a few here; warmer average temperature and increased storm, drought and heat wave intensity. Add to this sea level rise, the oceans becoming warmer and more acidic, and a host of other changes, some perhaps even as yet unseen. The onset of these environmental changes is expected to unleash a series of social and economic changes, which will add to the pain. A short list includes rising insurance premiums due to floods, wildfires and sea level rise, rising food costs prices as a result of crop failures due to drought and flood, homes and forests destroyed due to wildfires, and fisheries collapse due to warming seas and algal blooms. Perhaps the most frightening is the human migration that will follow when people’s homelands become too hot or dry to live in, or go underwater due to sea level rise. Where will these people go in our already crowded world?
This is why we need to act, as early as we can, to prevent more damage down the road and preserve this planet for generations to come. We can take pride in the fact that New Zealand is leading other nations in acting on climate change, by limiting greenhouse gas emissions with an emissions trading scheme and through programs to sequester atmospheric carbon dioxide in new forests. As a nation and as individuals, we can make a difference.
At the Marlborough Earth Day party, held at A & P showgrounds last April, a number of visitors were asked if there were aspects of climate change that they didn’t understand. Shannon asked, “Why does global warming lead to more climate variability?”
This is a good question because it isn’t immediately apparent why simple warming of the planet should lead to greater variability in our weather. Global warming – the gradual warming of our atmosphere due to build-up of heat trapping gases – is having both direct and subtle effects on short-term weather events and the climate over relatively long periods of time. The direct effects are easy to visualise; a warmer atmosphere leads, on average, to a warmer climate worldwide. At high latitudes – the Arctic and Antarctic – this has resulted in widespread melting of land and sea ice. At low latitudes, near the equator, it has led to some extreme heat waves, like those recently experienced in India and Pakistan. More subtle effects include global warming’s contribution to water evaporation and to changes in both air and sea currents.
The impact of global warming on water evaporation lead both to more intense rainfall and more severe droughts. Warm air can hold more moisture than cool air, so the evaporation of water from both land and sea is enhanced by warmer air temperatures. And since what goes up must come down, more moisture in the atmosphere results in more rainfall. For example, the extensive flooding in the south central US as a result of Hurricane Harvey last year can be related to rising sea surface temperatures in the Caribbean Sea, feeding more moisture to the storm than otherwise. Conversely, in places where it doesn’t rain, warmer air temperatures result in water evaporating from land more readily, resulting in more severe drought. The hotter it gets, the faster soil dries out.
Less apparent is how the very cold winter storms experienced by Europe and North America last winter can be related to global warming. Although research is ongoing, it appears to be due to a weakening of the northern jet stream – a river of air moving around the planet at the mid-latitudes. In the winter months, this brings a succession of Pacific storms to the west coast of North America. The jet stream also surrounds and bottles up cold air in the Arctic (the polar vortex), preventing it from breaking out into the mid-latitudes. It seems that as our climate has warmed, the jet stream has weakened, allowing both cold Arctic air to escape south and relatively warm southern air to stream north into the Arctic. While Europe and North America were freezing under unusually cold weather last winter, some areas of the Arctic experienced unusually warm winter weather. Temperatures in parts of the Arctic averaged 20ºC warmer than usual – the warmest Arctic winter temperatures on record.
In the long term, global warming could have an even more dramatic effect on climate. Scientists have noticed a weakening in a portion of the Gulf Stream that heads into the North Atlantic Ocean and this weakening appears to be related to Arctic warming. The Gulf Stream is a clockwise current of warm tropical water in the mid-Atlantic Ocean between Europe and North America. A portion of this current flows into the North Atlantic, keeping Northern Europe warmer than it would otherwise be, based upon its latitude on the planet. For example, the UK, while at the same latitude as Labrador and southern Alaska, does not share their far colder climates. It is this northern portion of the Gulf Stream that keeps the UK and the rest of Northern Europe warmer than they would be otherwise, so a weakening of this current would result in a cooler climate for Northern Europe – the opposite to what we might expect with global warming.
The Blog posts are a collection of opinion articles written by CKM member Tom Powell for the Marlborough Express. Tom is a retired geologist who came to New Zealand in 2004 to work in the geothermal industry on the North Island, is a New Zealand citizen and now lives in Blenheim.