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Global climate change can be understood by analyzing past historical climate data, such as atmospheric CO2 concentrations in ice cores.
- Evaluate the evidence for global climate change
- Climate change can be understood by approaching three areas of study: (1) current and past global climate change, (2) causes of past and present-day global climate change, and (3) ancient and current results of climate change.
- Since we cannot go back in time to directly measure climatic variables, such as average temperature and precipitation, we must rely on historical evidence of earth’s past climate, such as Antarctic ice cores.
- Three significant temperature anomalies, or irregularities, have occurred in the last 2000 years: the Medieval Climate Anomaly (or the Medieval Warm Period), the Little Ice Age, and the Industrial Era.
- With the beginning of the Industrial Era, atmospheric carbon dioxide began to rise.
- fossil fuel: any fuel derived from hydrocarbon deposits such as coal, petroleum, natural gas, and, to some extent, peat; these fuels are irreplaceable; their burning generates the greenhouse gas carbon dioxide
Global Climate Change
Climate change can be understood by approaching three areas of study: (1) evidence of current and past global climate change, (2) causes of past and present-day global climate change, and (3) ancient and current results of climate change.
It is helpful to keep these three different aspects of climate change clearly separated when consuming media reports about global climate change. It is common for reports and discussions about global climate change to confuse the data showing that earth’s climate is changing with the factors that drive this climate change.
Evidence for Global Climate Change
Since scientists cannot go back in time to directly measure climatic variables, such as average temperature and precipitation, they must, instead, indirectly measure temperature. To do this, scientists rely on historical evidence of earth’s past climates.
Antarctic ice cores are a key example of such evidence. These ice cores are samples of polar ice obtained by means of drills that reach thousands of meters into ice sheets or high mountain glaciers. Viewing the ice cores is like traveling backwards through time; the deeper the sample, the earlier the time period. Trapped within the ice are bubbles of air and other biological evidence that can reveal temperature and carbon dioxide data. Antarctic ice cores have been collected and analyzed to indirectly estimate the temperature of the earth over the past 400,000 years.
Before the late 1800s, the earth had been as much as 9°C cooler and about 3°C warmer. Atmospheric concentration of carbon dioxide also rose and fell in periodic cycles; note the relationship between carbon dioxide concentration and temperature. Carbon dioxide levels in the atmosphere have historically cycled between 180 and 300 parts per million (ppm) by volume.
Two significant temperature anomalies, or irregularities, have occurred in the last 2000 years. These are the Medieval Climate Anomaly (or the Medieval Warm Period) and the Little Ice Age. A third temperature anomaly aligns with the Industrial Era. The Medieval Climate Anomaly occurred between 900 and 1300 AD. During this time period, many climate scientists think that slightly-warmer conditions prevailed in many parts of the world; the higher-than-average temperature changes varied between 0.10 °C and 0.20 °C above the norm. Although 0.10 °C does not seem large enough to produce any noticeable change, it did free seas of ice. Because of this warming, the Vikings were able to colonize Greenland.
The Little Ice Age was a cold period that occurred between 1550 AD and 1850 AD. During this time, a slight cooling of a little less than 1 °C was observed in North America, Europe, and possibly other areas of the world. This 1 °C change is a seemingly-small deviation in temperature (as was observed during the Medieval Climate Anomaly); however, it also resulted in noticeable changes. Historical accounts reveal a time of exceptionally-harsh winters with much snow and frost.
Evidence of Climate Change
The main sources for evidence of global climate change are temperature increase in the atmosphere, rising sea levels, and the shrinking of Earth’s glaciers and ice caps.
Climate studies focused on the most recent centuries have evidenced a warming trend in the surface of the Earth. Between the years 1880 and 2012 the average temperature of the Earth’s surface has risen by 0.85°C (1.53°F), as shown in Figure 7. Additionally, this warming trend has been accelerating over time. For example, the rate of warming over the 50 years from 1956 to 2005 is 0.128°C per decade―nearly twice that of the 0.074°C per decade rate of increase for the 100 years between 1906 and 2005. This increase in Earth’s average surface temperature is what we call global warming
Global warming is the term used to describe an increase in the average temperature of the Earth's atmosphere and its oceans, a change that is believed to be permanently altering the Earth’s climate. The scientific consensus on climatic change related to global warming is that the average temperature of the Earth has risen between 0.4 and 0.8 °C over the past 100 years. The increased volumes of carbon dioxide and other greenhouse gases released by the burning of fossil fuels, land clearing, agriculture, and other human activities, are the primary causes of the global warming that has occurred over the past 50 years.
(adapted from) http://www.livescience.com/topics/global-warming/ .
Figure 7: Annual global average observed temperatures (black dots) along with simple fits to the data. The left hand axis shows anomalies relative to the 1961 to 1990 average and the right hand axis shows the estimated actual temperature (°C). Linear trend fits to the last 25 (yellow), 50 (orange), 100 (purple) and 150 years (red) are shown. Note that for shorter recent periods, the slope is greater, indicating accelerated warming.1
PCC, 2013: Climate Change 2013: The Physical Science Basis. Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, FAQ 2.1, Figure 1 FAQ 3.1, Figure 1. [Stocker,T.F., D.Qin, G.-K. Plattner, M.Tignor, S.K.Allen, J.Boschung, A.Nauels, Y.Xia, V.Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, UK and New York, USA.
The global temperature increase is greater at higher northern latitudes, as shown by the red-orange shading in Figure 8. This is due to several causes, including the greater buffering effect of larger, more extensive oceans in the southern latitudes, and the higher incidence of positive feedbacks in northern latitudes.
Figure 8: Global temperature anomalies for 2000 to 2009. Temperature anomalies do not depict absolute temperature, but rather how much warmer or colder a region is compared to the norm for that region from 1951 to 1980. Global temperatures from 2000–2009 were on average about 0.6°C higher than they were from 1951– 1980. The Arctic, however, was about 2°C warmer.1
By NASA images by Robert Simmon, based on data from the Goddard Institute for Space Studies. [Public domain], via Wikimedia Commons
One of those feedbacks is referred to as “ Arctic Amplification Arctic amplification refers to the greater rate of climate warming in the Arctic region than the rest of the world. The amount of land in the Northern Hemisphere allows for greater annual variation of snow cover. This fact allows for greater cooling and warming potentials when the overall climate forcing is altered. Less forcing would result in a cooling trend that would allow more snow cover and therefore a polar de-amplification effect in relation to the average temperature of the rest of the globe. More forcing, as is what happens under the influence of higher concentrations of greenhouse gases, allows for a more rapid decrease in snow and ice cover. The decrease of melting of snow and ice reduces the albedo reflectance of the poles therefore amplifying the temperature in the polar region. .” This phenomenon occurs because warmer temperatures cause snow to melt in northern regions. Loss of snow cover on the surface of the Earth due to snowmelt changes the color of the Arctic from white to dark, which decreases Earth’s albedo―the reflection of solar energy by Earth’s surface back to outer space. As a result, more sunlight is absorbed into the surface of the Earth, which causes further heating of the land and air in polar and mountainous regions. The positive feedback loop causes an amplification of polar warming. People living in northern countries, such as the Mongolian herders discussed is the case study at the beginning of this chapter, are trying to cope with the results of Arctic Amplification today.
Sea Level Rise
Figure 9. Changes in global average sea level since 1880. Data from coastal tide gauges and satellite altimeter observations were combined to provide the blue line (averages) and shaded blue area (depicting the variability). Changes since 1993 from satellite altimeter data alone are in red.1
The increase in sea level is another source of empirical evidence of climate change which is consistent with global warming. In the last century, the global average sea level rose 1.7 millimeters (0.067 inches) per year.
Effects of global warming
The signs of global warming are everywhere, and are more complex than just climbing temperatures.
CAUSES AND EFFECTS OF CLIMATE CHANGE
The planet is warming, from North Pole to South Pole. Since 1906, the global average surface temperature has increased by more than 1.6 degrees Fahrenheit (0.9 degrees Celsius)—even more in sensitive polar regions. And the impacts of rising temperatures aren’t waiting for some far-flung future–the effects of global warming are appearing right now. The heat is melting glaciers and sea ice, shifting precipitation patterns, and setting animals on the move.
Many people think of global warming and climate change as synonyms, but scientists prefer to use “climate change” when describing the complex shifts now affecting our planet’s weather and climate systems. Climate change encompasses not only rising average temperatures but also extreme weather events, shifting wildlife populations and habitats, rising seas, and a range of other impacts. All of these changes are emerging as humans continue to add heat-trapping greenhouse gases to the atmosphere.
Scientific Consensus: Earth's Climate Is Warming
Temperature data showing rapid warming in the past few decades, the latest data going up to 2020. According to NASA data, 2016 and 2020 are tied for the warmest year since 1880, continuing a long-term trend of rising global temperatures. The 10 warmest years in the 141-year record have occurred since 2005, with the seven most recent years being the warmest. Credit: NASA's Goddard Institute for Space Studies.
Multiple studies published in peer-reviewed scientific journals 1 show that 97 percent or more of actively publishing climate scientists agree*: Climate-warming trends over the past century are extremely likely due to human activities. In addition, most of the leading scientific organizations worldwide have issued public statements endorsing this position. The following is a partial list of these organizations, along with links to their published statements and a selection of related resources.
AMERICAN SCIENTIFIC SOCIETIES
Statement on Climate Change from 18 Scientific Associations
"Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver." (2009) 2
"Based on well-established evidence, about 97% of climate scientists have concluded that human-caused climate change is happening." (2014) 3
"The Earth&rsquos climate is changing in response to increasing concentrations of greenhouse gases (GHGs) and particulate matter in the atmosphere, largely as the result of human activities." (2016-2019) 4
"Based on extensive scientific evidence, it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. There is no alterative explanation supported by convincing evidence." (2019) 5
"Our AMA . supports the findings of the Intergovernmental Panel on Climate Change&rsquos fourth assessment report and concurs with the scientific consensus that the Earth is undergoing adverse global climate change and that anthropogenic contributions are significant." (2019) 6
"Research has found a human influence on the climate of the past several decades . The IPCC (2013), USGCRP (2017), and USGCRP (2018) indicate that it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-twentieth century." (2019) 7
"Earth's changing climate is a critical issue and poses the risk of significant environmental, social and economic disruptions around the globe. While natural sources of climate variability are significant, multiple lines of evidence indicate that human influences have had an increasingly dominant effect on global climate warming observed since the mid-twentieth century." (2015) 8
"The Geological Society of America (GSA) concurs with assessments by the National Academies of Science (2005), the National Research Council (2011), the Intergovernmental Panel on Climate Change (IPCC, 2013) and the U.S. Global Change Research Program (Melillo et al., 2014) that global climate has warmed in response to increasing concentrations of carbon dioxide (CO2) and other greenhouse gases . Human activities (mainly greenhouse-gas emissions) are the dominant cause of the rapid warming since the middle 1900s (IPCC, 2013)." (2015) 9
International Academies: Joint Statement
"Climate change is real. There will always be uncertainty in understanding a system as complex as the world&rsquos climate. However there is now strong evidence that significant global warming is occurring. The evidence comes from direct measurements of rising surface air temperatures and subsurface ocean temperatures and from phenomena such as increases in average global sea levels, retreating glaciers, and changes to many physical and biological systems. It is likely that most of the warming in recent decades can be attributed to human activities (IPCC 2001)." (2005, 11 international science academies) 10
"Scientists have known for some time, from multiple lines of evidence, that humans are changing Earth&rsquos climate, primarily through greenhouse gas emissions." 11
U.S. GOVERNMENT AGENCIES
"Earth&rsquos climate is now changing faster than at any point in the history of modern civilization, primarily as a result of human activities." (2018, 13 U.S. government departments and agencies) 12
&ldquoWarming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.&rdquo 13
&ldquoHuman influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems.&rdquo 14
List of Worldwide Scientific Organizations
The following page lists the nearly 200 worldwide scientific organizations that hold the position that climate change has been caused by human action.
*Technically, a &ldquoconsensus&rdquo is a general agreement of opinion, but the scientific method steers us away from this to an objective framework. In science, facts or observations are explained by a hypothesis (a statement of a possible explanation for some natural phenomenon), which can then be tested and retested until it is refuted (or disproved).
As scientists gather more observations, they will build off one explanation and add details to complete the picture. Eventually, a group of hypotheses might be integrated and generalized into a scientific theory, a scientifically acceptable general principle or body of principles offered to explain phenomena.
Quotation from page 6: "The number of papers rejecting AGW [Anthropogenic, or human-caused, Global Warming] is a miniscule proportion of the published research, with the percentage slightly decreasing over time. Among papers expressing a position on AGW, an overwhelming percentage (97.2% based on self-ratings, 97.1% based on abstract ratings) endorses the scientific consensus on AGW.&rdquo
Quotation from page 3: "Among abstracts that expressed a position on AGW, 97.1% endorsed the scientific consensus. Among scientists who expressed a position on AGW in their abstract, 98.4% endorsed the consensus.&rdquo
W. R. L. Anderegg, &ldquoExpert Credibility in Climate Change,&rdquo Proceedings of the National Academy of Sciences Vol. 107 No. 27, 12107-12109 (21 June 2010) DOI: 10.1073/pnas.1003187107.
P. T. Doran & M. K. Zimmerman, "Examining the Scientific Consensus on Climate Change," Eos Transactions American Geophysical Union Vol. 90 Issue 3 (2009), 22 DOI: 10.1029/2009EO030002.
9 Things We Learned From Leonardo DiCaprio's Climate Change Film
**Nov. 11, 2016 Update: "Before the Flood" is no longer available on YouTube for free, but you can see it on the following streaming platforms: Amazon Video, Vudu, YouTube ($2.99), Google Play ($2.99), and Hulu.
Ever since the late ‘90s, Leonardo DiCaprio has been talking about a warming atmosphere, rising sea levels, forest fires, and endangered wildlife. His new, free-to-stream documentary, “Before the Flood,” is in many ways a culmination of his advocacy. It’s an attempt to zoom out of the daily bombardment of news stories to help people appreciate the scale of climate change.
Trying to understand the problem bit by bit is, as the NASA astronaut Piers Seller says in the film, “like being an ant trying to understand how an elephant looks by crawling all over the elephant.”
So DiCaprio darts around the globe to give people as broad a view as possible. He travels to the Sumatran rainforest, at-risk island nations, the Arctic, Greenland, India, China, Miami, and many other places that are being disrupted by climate change right now.
Here are nine takeaways from that journey:
1) Greenland and the Arctic are on track to melt entirely.
Greenland is close to entering an irreversible feedback loop of melting. Ice reflects sunlight water absorbs sunlight. As more of the country’s ice turns to water, more sunlight is absorbed, causing more heating, causing more melting, and so on. If Greenland were to melt, it alone would raise global sea levels by several feet.
The Arctic “is like the air conditioning for the Northern Hemisphere,” says Dr. Enric Sala in the film. “If it goes away, that’s going to change currents, that’s going to change weather patterns, it’s going to make droughts more catastrophic.”
2) The last time the Earth was four degrees celsius warmer was 4 million years ago.
Current trends suggest that the Earth will warm by more than 4 degrees through man-made climate change. This will lead to catastrophic droughts, the collapse of agricultural belts, the collapse of marine ecosystems, severe storms, and much more.
3) 50% of all coral has been lost in the past 30 years.
As oceans absorb CO2, they become warmer and go through a process of acidification. Both events make it harder for coral reefs to form and stay alive. It’s likely that reefs will vanish in the decades ahead, reversing a billion years of evolution.
Coral reefs are incredibly vibrant ecosystems, fostering a vast range of species and providing food for a billion people around the world. If they collapse, that means a billion people will have to find an alternative source of food.
4) 700 million Indians cook with biomass, aka cow dung.
Because electricity and access to sources of heat are unavailable to hundreds of millions of Indians, they cook food with cow dung that generates heat. This means that there are 700 million people not yet relying on electricity for this task. Putting all of these people “on the grid” will dramatically increase its environmental impact — unless the shift is made with sustainable energy.
5) Cows are environmentally hazardous.
Cows both consume a lot of resources, and emit lots of dangerous greenhouse gases. In the US, 47% of land is dedicated to food production. Seventy percent of this land is used to grow feed for cattle. Conversely, 1% of that land is used to grow crops for humans.
Cows continuously emit methane, a greenhouse gas 23 times more potent than carbon, as they go about their days.
6) China is the world’s biggest polluter, but it also invests the most in sustainable energy.
Partly because of large-scale social unrest, the Chinese government is rapidly investing in renewable energy. In 2015, China accounted for 36% of the world’s investments in renewables.
7) Elon Musk has a plan.
Elon Musk is building a gigafactory with Tesla that will produce an enormous amount of sustainable energy when completed. One hundred such factories could power the entire world, according to Musk, but Tesla can’t build them all alone.
8) Despite scientific evidence, not everyone believes in climate change and that has slowed action.
9) You can make a difference.
While addressing climate change depends on making deep structural changes to the world’s economies — such as ending fossil fuel extraction — people can accelerate the process in their own lives.
— Don’t buy products with palm oil because palm oil production drives deforestation
So what's the evidence?
The research falls into nine independently studied, but physically related, lines of evidence:
- Simple chemistry – When we burn carbon-based materials, carbon dioxide (CO2) is emitted (research beginning in the 1900s).
- Basic accounting of what we burn, and therefore how much CO2 we emit (data collection beginning in the 1970s).
- Measuring CO2 and other greenhouse gases in the atmosphere and trapped in ice to find they are increasing, with levels higher than anything we've seen in nearly a million years (measurements beginning in the 1950s).
- Chemical analysis of the atmospheric CO2 that reveals the increase is coming from burning fossil fuels (research beginning in the 1950s).
- Basic physics that shows us that CO2 absorbs heat (research beginning in the 1820s).
- Monitoring climate conditions to find that the air, sea and land is warming, as we would expect with rising greenhouse gas emissions as a response, ice is melting and sea level is rising (research beginning in the 1930s).
- Ruling out natural factors that can influence climate like the sun and ocean cycles (research beginning in the 1830s).
- Employing computer models to run experiments of natural versus human-influenced simulations of Earth (research beginning in the 1960s).
- Consensus among scientists who consider all previous lines of evidence and make their own conclusions (polling beginning in the 1990s).
Climate study finds evidence of global shift in the 1980s
Planet Earth experienced a global climate shift in the late 1980s on an unprecedented scale, fuelled by anthropogenic warming and a volcanic eruption, according to new research published this week.
Scientists say that a major step change, or 'regime shift', in Earth's biophysical systems, from the upper atmosphere to the depths of the ocean and from the Arctic to Antarctica, was centred around 1987, and was sparked by the El Chichón volcanic eruption in Mexico five years earlier.
Their study, published in Global Change Biology, documents a range of associated events caused by the shift, from a 60% increase in winter river flow into the Baltic Sea to a 400% increase in the average duration of wildfires in the Western United States. It also suggests that climate change is not a gradual process, but one subject to sudden increases, with the 1980s shift representing the largest in an estimated 1,000 years.
Philip C. Reid, Professor of Oceanography at Plymouth University's Marine Institute, and Senior Research Fellow at the Sir Alister Hardy Foundation for Ocean Science (SAHFOS), is the lead author of the report, Global impacts of the 1980s regime shift.
"We demonstrate, based on 72 long time series, that a major change took place in the world centred on 1987 that involved a step change and move to a new regime in a wide range of Earth systems," said Professor Reid.
"Our work contradicts the perceived view that major volcanic eruptions just lead to a cooling of the world. In the case of the regime shift it looks as if global warming has reached a tipping point where the cooling that follows such eruptions rebounds with a rapid rise in temperature in a very short time. The speed of this change has had a pronounced effect on many biological, physical and chemical systems throughout the world, but is especially evident in the Northern temperate zone and Arctic."
Over the course of three years, the scientists -- drawing upon a range of climate models, using data from nearly 6,500 meteorological stations, and consulting innumerable scientists and their studies round the world -- found evidence of the shift across a wide range of biophysical indicators, such as the temperature and salinity of the oceans, the pH level of rivers, the timing of land events, including the behaviour of plants and birds, the amount of ice and snow in the cryosphere (the frozen world), and wind speed changes.
They detected a marked decline in the growth rate of CO2 in the atmosphere after the regime shift, coinciding with a sudden growth in land and ocean carbon sinks -- such as new vegetation spreading into polar areas previously under ice and snow. And they found that the annual timing of the regime shift appeared to have moved regionally around the world from west to east, starting with South America in 1984, North America (1985), North Atlantic (1986), Europe (1987), and Asia (1988).
These dates coincide with significant shifts to an earlier flowering date for cherry trees around Earth in Washington DC, Switzerland, and Japan and coincided with the first evidence of the extinction of amphibians linked to global warming, such as the harlequin frog and golden toad in Central and South America.
Second author Renata E. Hari, Eawag, Dübendorf, Switzerland, said: "The 1980s regime shift may be the beginning of the acceleration of the warming shown by the IPCC. It is an example of the unforeseen compounding effects that may occur if unavoidable natural events like major volcanic eruptions interact with anthropogenic warming."
9.4 Signaling in Single-Celled Organisms
By the end of this section, you will be able to do the following:
- Describe how single-celled yeasts use cell signaling to communicate with one another
- Relate the role of quorum sensing to the ability of some bacteria to form biofilms
Within-cell signaling allows bacteria to respond to environmental cues, such as nutrient levels. Some single-celled organisms also release molecules to signal to each other.
Signaling in Yeast
Yeasts are eukaryotes (fungi), and the components and processes found in yeast signals are similar to those of cell-surface receptor signals in multicellular organisms. Budding yeasts (Figure 9.16) are able to participate in a process that is similar to sexual reproduction that entails two haploid cells (cells with one-half the normal number of chromosomes) combining to form a diploid cell (a cell with two sets of each chromosome, which is what normal body cells contain). In order to find another haploid yeast cell that is prepared to mate, budding yeasts secrete a signaling molecule called mating factor . When mating factor binds to cell-surface receptors in other yeast cells that are nearby, they stop their normal growth cycles and initiate a cell signaling cascade that includes protein kinases and GTP-binding proteins that are similar to G-proteins.
Signaling in Bacteria
Signaling in bacteria enables bacteria to monitor extracellular conditions, ensure that there are sufficient amounts of nutrients, and ensure that hazardous situations are avoided. There are circumstances, however, when bacteria communicate with each other.
The first evidence of bacterial communication was observed in a bacterium that has a symbiotic relationship with Hawaiian bobtail squid. When the population density of the bacteria reaches a certain level, specific gene expression is initiated, and the bacteria produce bioluminescent proteins that emit light. Because the number of cells present in the environment (cell density) is the determining factor for signaling, bacterial signaling was named quorum sensing . In politics and business, a quorum is the minimum number of members required to be present to vote on an issue.
Quorum sensing uses autoinducers as signaling molecules. Autoinducers are signaling molecules secreted by bacteria to communicate with other bacteria of the same kind. The secreted autoinducers can be small, hydrophobic molecules, such as acyl-homoserine lactone (AHL), or larger peptide-based molecules each type of molecule has a different mode of action. When AHL enters target bacteria, it binds to transcription factors, which then switch gene expression on or off. When the number of bacteria increases so does the concentration of the autoinducer, triggering increased expression of certain genes including autoinducers, which results in a self-amplifying cycle, also known as a positive feedback loop (Figure 9.17). The peptide autoinducers stimulate more complicated signaling pathways that include bacterial kinases. The changes in bacteria following exposure to autoinducers can be quite extensive. The pathogenic bacterium Pseudomonas aeruginosa has 616 different genes that respond to autoinducers.
Some species of bacteria that use quorum sensing form biofilms, complex colonies of bacteria (often containing several species) that exchange chemical signals to coordinate the release of toxins that will attack the host. Bacterial biofilms (Figure 9.18) can sometimes be found on medical equipment when biofilms invade implants such as hip or knee replacements or heart pacemakers, they can cause life-threatening infections.
Which of the following statements about quorum sensing is false?
- Autoinducer must bind to receptor to turn on transcription of genes responsible for the production of more autoinducer.
- The receptor stays in the bacterial cell, but the autoinducer diffuses out.
- Autoinducer can only act on a different cell: it cannot act on the cell in which it is made.
- Autoinducer turns on genes that enable the bacteria to form a biofilm.
What advantage might biofilm production confer on the S. aureus inside the catheter?
Research on the details of quorum sensing has led to advances in growing bacteria for industrial purposes. Recent discoveries suggest that it may be possible to exploit bacterial signaling pathways to control bacterial growth this process could replace or supplement antibiotics that are no longer effective in certain situations.
Link to Learning
Watch geneticist Bonnie Bassler discuss her discovery of quorum sensing in biofilm bacteria in squid.
Cellular Communication in Yeasts
The first cellular form of life on our planet likely consisted of single-celled prokaryotic organisms that had limited interaction with each other. While some external signaling occurs between different species of single-celled organisms, the majority of signaling within bacteria and yeasts concerns only other members of the same species. The evolution of cellular communication is an absolute necessity for the development of multicellular organisms, and this innovation is thought to have required approximately 2 billion years to appear in early life forms.
Yeasts are single-celled eukaryotes and, therefore, have a nucleus and organelles characteristic of more complex life forms. Comparisons of the genomes of yeasts, nematode worms, fruit flies, and humans illustrate the evolution of increasingly complex signaling systems that allow for the efficient inner workings that keep humans and other complex life forms functioning correctly.
Kinases are a major component of cellular communication, and studies of these enzymes illustrate the evolutionary connectivity of different species. Yeasts have 130 types of kinases. More complex organisms such as nematode worms and fruit flies have 454 and 239 kinases, respectively. Of the 130 kinase types in yeast, 97 belong to the 55 subfamilies of kinases that are found in other eukaryotic organisms. The only obvious deficiency seen in yeasts is the complete absence of tyrosine kinases. It is hypothesized that phosphorylation of tyrosine residues is needed to control the more sophisticated functions of development, differentiation, and cellular communication used in multicellular organisms.
Because yeasts contain many of the same classes of signaling proteins as humans, these organisms are ideal for studying signaling cascades. Yeasts multiply quickly and are much simpler organisms than humans or other multicellular animals. Therefore, the signaling cascades are also simpler and easier to study, although they contain similar counterparts to human signaling. 2
Link to Learning
Watch this collection of interview clips with biofilm researchers in “What Are Bacterial Biofilms?”
What Can Trees Tell Us About Climate Change?
But to understand what the trees tell us, we first have to understand the difference between weather and climate.
Weather is a specific event—like a rain storm or hot day—that happens over a short period of time. Weather can be tracked within hours or days. Climate is the average weather conditions in a place over a long period of time (30 years or more).
Scientists at the National Weather Service have been keeping track of weather in the United States since 1891. But trees can keep a much longer record of Earth’s climate. In fact, trees can live for hundreds—and sometimes even thousands—of years!
One way that scientists use trees to learn about past climate is by studying a tree’s rings. If you’ve ever seen a tree stump, you probably noticed that the top of the stump had a series of rings. It looks a bit like a bullseye.
The light and dark rings of a tree. Image credit: Flickr Creative Commons user Amanda Tromley
These rings can tell us how old the tree is, and what the weather was like during each year of the tree’s life. The light-colored rings represent wood that grew in the spring and early summer, while the dark rings represent wood that grew in the late summer and fall. One light ring plus one dark ring equals one year of the tree’s life.
The color and width of tree rings can provide snapshots of past climate conditions.
Because trees are sensitive to local climate conditions, such as rain and temperature, they give scientists some information about that area’s local climate in the past. For example, tree rings usually grow wider in warm, wet years and they are thinner in years when it is cold and dry. If the tree has experienced stressful conditions, such as a drought, the tree might hardly grow at all in those years.
Scientists can compare modern trees with local measurements of temperature and precipitation from the nearest weather station. However, very old trees can offer clues about what the climate was like long before measurements were recorded.
This is said to be the Methuselah Tree, one of the oldest living trees in the world. Methuselah, a bristlecone pine tree in White Mountain, California is thought to be almost 5,000 years old. Image credit: Oke/Wikimedia Commons
In most places, daily weather records have only been kept for the past 100 to 150 years. So, to learn about the climate hundreds to thousands of years ago, scientists need to use other sources, such as trees, corals, and ice cores (layers of ice drilled out of a glacier).
Do you have to cut down a tree to see the rings?
No way! You can count the rings of a tree by collecting a sample with an instrument called an increment borer. The borer extracts a thin strip of wood that goes all the way to the center of the tree. When you pull the strip out, you can count the rings on the strip of wood and the tree is still as healthy as can be!
A student learns how to take a tree core sample with an increment borer in the Manti-LaSal National Forest in Utah. Image credit: USDA
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