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Once carbon dioxide concentrations became low enough (around 300 parts per million) between two and three million years ago, the current ice age cycle began. sodar99 / Getty Images
By James Renwick
Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.
If you have a question you'd like an expert to answer, please send it to climate.change@stuff.co.nz
Earth had several periods of high carbon dioxide levels in the atmosphere and high temperatures over the last several million years. Can you explain what caused these periods, given that there was no burning of fossil fuels or other sources of human created carbon dioxide release during those times?
Burning fossil fuels or vegetation is one way to put carbon dioxide into the air – and it is something we have become very good at. Humans are generating nearly 40 billion tons of carbon dioxide every year, mostly by burning fossil fuels.
<p>Carbon dioxide stays in the air <a href="https://earthobservatory.nasa.gov/features/CarbonCycle/page5.php" target="_blank">for centuries to millennia</a> and it builds up over time. Since we began the systematic use of coal and oil for fuel, around 300 years ago, the amount of carbon dioxide in the air has gone up by almost half.</p>
<img lazy-loadable="true" src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzI4MTk4NC9vcmlnaW4uZ2lmIiwiZXhwaXJlc19hdCI6MTYxNzUxNDc5NH0.GxG5zlOmzrFahpUrC6MNCzaw70WWCEHhcH2XF8A-17M/img.gif?width=980" id="fbe04" class="rm-shortcode" data-rm-shortcode-id="8a3d03f2b40ceab9b18c3ef63a5774cf" data-rm-shortcode-name="rebelmouse-image" />
<p>Apart from the emissions we add, carbon dioxide concentrations in the air go up and down as part of the natural <a href="https://earthobservatory.nasa.gov/features/CarbonCycle" target="_blank">carbon cycle</a>, driven by exchanges between the air, the oceans and the biosphere (life on earth), and ultimately by geological processes.</p>
Natural Changes in Carbon Dioxide
<p>Every year, carbon dioxide concentrations rise and fall a little as plants grow in spring and summer and die off in the autumn and winter. The timing of this <a href="https://niwa.co.nz/atmosphere/our-data/trace-gas-plots/carbon-dioxide" target="_blank">seasonal rise and fall</a> is tied to northern hemisphere seasons, as most of the land surface on Earth is there.</p><p>The oceans also play an active role in the carbon cycle, contributing to variations over a few months to slow shifts over centuries. Ocean water takes up carbon dioxide directly in an exchange <a href="https://sos.noaa.gov/datasets/ocean-atmosphere-co2-exchange/" target="_blank">between the air and seawater</a>. Tiny marine plants use carbon dioxide for photosynthesis and many microscopic marine organisms use carbon compounds to make shells. When these marine micro-organisms die and sink to the seafloor, they take the carbon with them.</p><p>Collectively, the biosphere (ecosystems on land and in soils) and the oceans are absorbing about <a href="https://worldoceanreview.com/en/wor-1/ocean-chemistry/co2-reservoir/" target="_blank">half of all human-emitted carbon dioxide</a>, and this slows the rate of climate change. But as the climate continues to change and the oceans warm up further, it is not clear whether the biosphere and oceans will continue absorbing such a large fraction of our emissions. As water warms, it is less able to absorb carbon dioxide, and as the climate changes, many ecosystems become stressed and are less able to photosynthesise carbon dioxide.</p>Earth’s Deep Climate History
<p>On time scales of hundreds of thousands to millions of years, carbon dioxide concentrations in the air have varied hugely, and so has global climate.</p><p>This <a href="https://www.skepticalscience.com/weathering.html" target="_blank">long-term carbon cycle</a> involves the formation and decay of the Earth's surface itself: tectonic plate activity, the build-up and weathering of mountain chains, prolonged volcanic activity, and the emergence of new seafloor at active mid-ocean faults.</p><p>Most of the carbon stored in the Earth's crust is in the form of limestone, created from the carbon-based shells of marine organisms that sank to the ocean floor millions of year ago.</p><p>Carbon dioxide is added to the air when volcanoes erupt, and it is taken out of the air as rocks and mountain ranges weather and wear down. These processes typically take millions of years to add or subtract carbon dioxide from the atmosphere.</p><p>In the present day, volcanoes add only a little carbon dioxide to the air, around <a href="https://www.skepticalscience.com/volcanoes-and-global-warming.htm" target="_blank">1% of what human activity is currently contributing</a>. But there have been times in the past where volcanic activity has been vastly greater and has spewed large amounts of carbon dioxide into the air.</p><p>An example is around 250 million years ago, when prolonged volcanic activity raised atmospheric carbon dioxide levels dramatically. These were volcanic eruptions on a vast scale - lasting for around two million years and <a href="https://www.sciencedaily.com/releases/2017/10/171002105227.htm" target="_blank">causing a mass extinction</a>.</p><p>In the more recent geological past, the past 50 million years, carbon dioxide levels have been gradually dropping overall and the climate has been cooling, with some ups and downs. Once carbon dioxide concentrations became low enough (around 300 parts per million) between two and three million years ago, the current ice age cycle began, but the warming our emissions are causing is larger than the natural cooling trend.</p><p>While Earth's climate has changed significantly in the past, it happened on geological time scales. The carbon in the oil and coal we burn represents carbon dioxide taken up by vegetation hundreds of millions of years ago and then deposited through geological processes over millennia. We have burned a significant proportion within a few centuries.</p><p>If human emissions of carbon dioxide continue to increase through this century, we could reach levels <a href="https://e360.yale.edu/features/how-the-world-passed-a-carbon-threshold-400ppm-and-why-it-matters" target="_blank">not seen for tens of millions of years</a>, when Earth had a much warmer climate with much higher sea levels and no ice sheets. </p>
<p><a href="https://theconversation.com/profiles/james-renwick-460484" target="_blank"><em style="">James Renwick</em></a><em> is a </em><em>Professor, Physical Geography (climate science) at Te Herenga Waka — Victoria University of Wellington.</em></p><p><em></em><em>Disclosure statement: </em><em>James Renwick receives funding from the NZ Ministry for Business, Innovation and Employment. He is affiliated with the NZ Climate Change Commission.</em></p><p><em>Reposted with permission from <a href="https://theconversation.com/climate-explained-what-caused-major-climate-change-in-the-past-137874" target="_blank">The Conversation</a>.</em></p>From Your Site Articles
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A view of the Piton de la Fournaise crater. Malavika Vyawahare
By Malavika Vyawahare
Giant tortoises and flying foxes once roamed La Réunion, a volcanic island off the eastern coast of Africa. Then humans arrived and decided to stay. Within 150 years of their appearance, large fruit-eating animals like the giant tortoises (Cylindraspis indica) and flying foxes (Pteropus niger), a type of bat, were wiped off the face of La Réunion.
<p>This speck of land in the western Indian Ocean, an overseas department of France, was one of the last corners of the planet to be colonized by humans. It is also home to the Piton de la Fournaise, one of the most active volcanoes in the world. It was recently in the throes of another eruption, having erupted almost 240 times since 1650.</p><p>The scars from these eruptions are <u><a href="https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2745.13359" target="_blank">now helping scientists uncover</a></u> the lasting effects of permanent human settlement on life on the island, including the loss of large-fruited trees like <em>Sideroxylon borbonicum</em>, known locally as <em>bois de fer de Bourbon</em>, and <em>Labourdonnaisia calophylloides</em>, or <em>bois de natte à petites feuilles</em>.</p><p>The fates of flora and fauna are linked. Animals and birds are important to plants; they help to disperse seeds, transporting them near and far. Which seeds and how far they get scattered depend on the kind of creatures that get their paws or beaks on the seeds. The largest fruit eater inhabiting the island today is the Réunion bulbul (<em>Hypsipetes borbonicus</em>), a bird a thousand times smaller than the now extinct giant tortoise. The bulbul can't feed on fruits that the tortoise could eat.</p><p>Not many would consider living in the shadow of an active volcano good fortune. For Sébastien Albert and his colleagues at the University of La Réunion, however, the frequency of eruptions at Piton de la Fournaise has proven providential. They recently published a paper in the <em>Journal of Ecology</em> describing the loss of large-fruited trees by creating a timeline over several centuries. Because the time of each eruption is known, it is possible to see how the plant community changed before and after human colonization.</p>
<p>Albert described the island as a "paradise" before humans established themselves there around the mid-17th century. The forests were dotted with towering trees that bore large, fleshy fruits enclosing chunky seeds. Seeds come in all sizes; the biggest in the world is the genitalia-shaped seed of the coco de mer (<em>Lodoicea maldivica</em>) found on Seychelles, an archipelago north of La Réunion. It can grow 30 centimeters (1 foot) across and weigh more than 15 kilograms (33 pounds). At the other end of the spectrum, some orchids produce seeds that are a fraction of a millimeter across, finer than a grain of sand.</p><p>The Réunion bulbul can only consume seeds smaller than 13 mm, or about half an inch. A larger species of bird native to La Réunion, the Mascarene parrot (<em>Mascarinus mascarin</em>), went extinct before the turn of the 19th century. So did the Réunion fruit pigeon (<em>Nesoenas duboisi</em>).</p><p>Throughout the Mascarenes — the Indian Ocean islands of Mauritius, Rodrigues (which is today part of Mauritius), and La Réunion — this is a familiar tale. The extinction of the dodo (<em>Raphus cucullatus</em>) in Mauritius is emblematic of creatures lost to human exploitation.</p>
<p>Overhunting, habitat loss and invasive predators contributed to the animals' disappearance. Giant tortoises were hunted by European sailors for their meat even before human habitation began. Their eggs fell prey to invasive species like pigs, cats and rats. Henri du Quesne, a French naval officer, wrote of the tortoises: "Their Flesh is very delicate; the Fat better than Butter or the best Oil, for all sorts of Sawces." Another account from 1671 noted that it was not possible to go six steps without coming upon one of these friendly giants. By 1800, they were all but gone.</p><p>The difficult part is linking their disappearance to impacts on tree diversity. "There is evidence for declines in large-seeded species that rely on large vertebrates for the dispersal of their seeds. Examples include Africa, Peru, and Brazil," said Elizabeth Wandrag, a plant ecologist at the University of New England, Australia, who was not involved in the study.</p><p>"It is not always possible to explicitly link the loss of large frugivores, and wholesale losses of species — many tree species that rely on large frugivores for dispersal are still present in forests that have lost those dispersers but have instead become more aggregated and/or show lower survival," Wandrag told Mongabay in an email.</p>
<p>Which is where the lava flows come in. Lava flow from a volcanic eruption is a major disturbance for any ecosystem; it tears through forests, burning everything in its path. It presents a kind of clean slate (literally) to see how plants recolonize. For existing forests, entangling the effects and even pinpointing the collapse of a species may not be as simple.</p><p>By studying how plant communities recovered after each eruption, the researchers realized that large-seeded species were not fully recovering because the fauna around them had changed since the previous eruption. "We analyzed 151 vegetation surveys on lava flows dated between 1401 AD and 1956 AD," the authors write in the paper. Tracking the changing vegetation over five centuries "has helped to pinpoint the important role that these lost animals played for these forests." The scientists say this is because when the animals that were best suited to disperse their seeds disappeared, the trees also started to fade away from the landscape.</p><p>"It was nice that the findings of this study mirrored some of those we have seen in our research on <u><a href="https://doi.org/10.1073/pnas.1709584114" target="_blank">Guam</a></u> without frugivores, some tree species simply aren't colonizing newly disturbed locations," Wandrag said. "In this case, the much longer history of defaunation, long-term chronosequence of plant communities, and botanical records allowed the authors to link that pattern to the resulting adult tree community."</p>
<p class=""><em>Reposted with permission from <a href="https://news.mongabay.com/2020/04/what-one-of-the-worlds-most-active-volcanoes-tells-us-about-missing-trees/" target="_blank">Mongabay</a>.</em></p>From Your Site Articles
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By Jason Bittel
Since Hawaii's Kilauea volcano began erupting in early May, we've been mesmerized, month after month, by videos depicting what can happen when molten rock dances through the air, forms gigantic rivers or crashes into a Ford Mustang.
<p>But some videos are much harder to watch—like those depicting the many homes destroyed or this one shot by Puna resident Travis Sanders in June. The footage shows a green sea turtle apparently trapped in a tidal pool known as Champagne Ponds in Kapoho Bay, as lava burns in the background and rocks seem to prevent the turtle from crawling onto land. When Sanders reached down to test the water, he said it felt to be near boiling.</p>
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<p>It's hard to say exactly how much heat a sea turtle can handle, said <a href="https://gstc.jekyllisland.com/about-us/our-staff/staff/" target="_blank">Terry Norton</a>, a veterinarian and director of the <a href="https://gstc.jekyllisland.com/" target="_blank">Georgia Sea Turtle Center</a>. "I would think that getting above 90 degrees Fahrenheit, they would start showing signs of heat stress, and definitely upper 90s and 100 would likely be eventually fatal," he said. "Hotter than that would definitely be fatal."<br></p><p>We don't know just how hot the water was in Kapoho Bay that night, but we do know what Sanders said happened next. After turning his camera off, he made a second attempt to save the turtle, but it was already too late.</p><p>"I tried to pull him out but his legs fell apart," <a href="http://www.staradvertiser.com/2018/07/25/breaking-news/puna-residents-criticize-dlnr-for-turtle-deaths/" target="_blank">Sanders told the Honolulu Star Advertiser</a>. "He was boiled alive."</p><p>In light of Sanders's video and several other reports of sea turtles trapped in ponds and lagoons, the state's Department of Land and Natural Resources (DLNR) issued a statement saying that it would conduct aerial surveys with helicopters to search for sea turtles. Thus far these searches have not spotted any others trapped by lava flows.</p><p>Sanders said he saw around 60 sea turtles gathering in an area near the Pohoiki boat ramp, just south of Kapoho Bay. (As of mid-August, the entire structure was surrounded by <a href="http://bigislandnow.com/2018/08/15/lagoon-created-at-pohoiki-new-map-of-lava-flow/" target="_blank">a wall of hardened lava</a>.) Another report from a local photographer documented <a href="http://www.hawaiinewsnow.com/story/38710696/turtles-marine-life-found-dead-on-pohoiki-shores-after-lava-approaches-area" target="_blank">six dead sea turtles</a> in July in the same vicinity.</p><p>According to Norton, most sea turtles, which are cold-blooded, should be able to sense these increases in heat and swim away in time. A <a href="https://www.khon2.com/news/local-news/videos-of-sea-turtles-trapped-by-lava-prompts-action-by-dlnr/1321868438" target="_blank">passage from the DLNR</a> statement concurs:</p><blockquote>"While it is unknown how many turtles may have lived in or around Kapoho or Pohoiki, it's believed most turtles had access to the open ocean via channels or open fish pond gates, and that they were able to swim away and save themselves before being harmed by the lava flow."<br></blockquote><p>But given the evidence that at least seven sea turtles did not escape, one has to wonder if many others might also be in harm's way. Despite declining numbers worldwide, green sea turtles are actually on the rise in Hawaii. Their population on the islands has increased by <a href="http://www.fpir.noaa.gov/PRD/prd_green_sea_turtle.html" target="_blank">53 percent over the past 25 years</a>—thanks in no small part to their <a href="http://www.fpir.noaa.gov/PRD/prd_green_sea_turtle.html" target="_blank">protection under the Endangered Species Act and Hawaiian state law</a>.</p><p>According to <a href="https://www.fisheries.noaa.gov/feature-story/look-back-scientist-dedicates-career-sea-turtles-hawaii" target="_blank">George Balazs</a>, who has spent the last 48 years studying sea turtles with the National Oceanic and Atmospheric Administration and the University of Hawaii, there is reason to hope that the eruption's toll on sea turtles may not be as bad as some fear. Green sea turtles do nest in the summer, but Balazs said "there are no green turtle nesting sites on the geologically active island of Hawaii." (The animals prefer the French Frigate Shoals, an atoll almost 800 miles to the northwest.) It is true that hawksbill turtles, which are <a href="http://www.iucnredlist.org/details/8005/0" target="_blank">critically endangered</a>, nest on Hawaii's mainland, however, and Balazs himself witnessed lava destroy some of those sites back in the early 1980s.</p><p>The bottom line, said Balazs, is that while sad, the lava-related deaths or injuries of a small number of unlucky animals is unlikely to significantly affect their population's continued recovery.</p><p> <em>Reposted with permission from our media associate <a href="https://www.nrdc.org/onearth/just-how-bad-was-hawaiis-volcanic-eruption-sea-turtles" target="_blank">onEarth</a>.</em><em></em></p>
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Mount Agung eruption on Nov. 28, 2017. I Gusti Bagus Sudiantara / Flickr
On Wednesday the Indonesian government opened an airport on Bali as wind blew away ash spewing out of a volcano, clearing the air for planes and giving residents and tourists a chance to escape.
In the past several days, the volcano has disrupted operations at Bali's airport, the second-busiest in Indonesia, while tens of thousands of residents living within a 10-kilometer radius of Mount Agung have been told to leave. Around 43,000 people had fled, but an estimated 90,000 to 100,000 people were still living in the eruption zone.
<p style="">Earlier in the week Indonesia's National Disaster Management Authority (BNPB) <a href="https://www.bnpb.go.id/home/detail/3540/AWAS-GUNUNG-AGUNG,-STATUS-DINAIKKAN-DARI-SIAGA-KE-AWAS" target="_blank">warned</a> that eruptions are increasing and declared the highest level of alert for a volcano. The BNPB warned that there is a large risk of lahar flows if the volcano erupts. Lahar flows are mudflows that contain volcanic debris and are capable of destroying everything in their path. President Joko Widodo begged residents living in the danger zone to move to emergency centers.<br></p><p style="">The last time Mount Agung erupted was in 1963, and the incident killed more than 1,000 people.</p><p style="">Outside Bali, scientists are waiting to see how the volcano affects the earth's temperature. "Most eruptions do not have a meaningful <a href="http://www.ecowatch.com/climate-change/">climate</a> impact, and so the risks associated with the eruption are limited to the nearby population," Chris Colose, a NASA climate scientist <a href="https://www.vox.com/energy-and-environment/2017/11/28/16712234/bali-volcano-eruption-agung-climate" target="_blank">told Vox</a>. "For climate, the big thing to pay attention [to] isn't the ash but the sulfur emissions." Sulfur dioxide reacts in the sky in such a way that it scatters sunlight and cools the planet. </p><p style="">The last time Mount Agung erupted it brought global temperatures down by between 0.1 and 0.2°C for a year. A climate researcher at <a href="https://www.carbonbrief.org/analysis-how-could-agung-volcano-bali-affect-global-temperature" target="_blank">Carbon Brief</a>, Zeke Hausfather, has showed that this round of eruptions could have a similar effect lasting until 2020. </p><p style="">On <a href="https://twitter.com/eruptionsblog/status/935209224820453378?ref_src=twsrc%5Etfw&ref_url=https%3A%2F%2Fwww.vox.com%2Fenergy-and-environment%2F2017%2F11%2F28%2F16712234%2Fbali-volcano-eruption-agung-climate" target="_blank">Twitter</a>, Erik Klemetti, a volcanologist at Denison University wrote, "the eruption at Agung in Indonesia has been relatively small so far, but with lava at the summit crater, it is anyone's guess how it proceeds from here."</p><p style="">See the video below for a live broadcast of the volcano:</p><p class="shortcode-media shortcode-media-youtube">
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