Our Common Home

If you haven't been living under a rock, you have no doubt heard that Pope Francis has finally released his encyclical on the environment, entitled Laudato Si' after its first two words. I cannot encourage you strongly enough to read it, or if its considerable length is too daunting, one of the stories summarizing it. It is a truly remarkable treatise on the modern human condition  worthy of being read and noted by everyone. I will only comment on it here briefly, since I have very little to add to Francis' challenge.

The beginning of the encyclical (paragraphs 1-2) quote the pope's namesake in the course of laying out his vision:

“LAUDATO SI’, mi’ Signore” – “Praise be to you, my Lord”. In the words of this beautiful canticle, Saint Francis of Assisi reminds us that our common home is like a sister with whom we share our life and a beautiful mother who opens her arms to embrace us. “Praise be to you, my Lord, through our Sister, Mother Earth, who sustains and governs us, and who produces various fruit with coloured flowers and herbs”.
This sister now cries out to us because of the harm we have inflicted on her by our irresponsible use and abuse of the goods with which God has endowed her. We have come to see ourselves as her lords and masters, entitled to plunder her at will. The violence present in our hearts, wounded by sin, is also reflected in the symptoms of sickness evident in the soil, in the water, in the air and in all forms of life. This is why the earth herself, burdened and laid waste, is among the most abandoned and maltreated of our poor; she “groans in travail” (Rom 8:22). We have forgotten that we ourselves are dust of the earth (cf. Gen 2:7); our very bodies are made up of her elements, we breathe her air and we receive life and refreshment from her waters.

He further uses Saint Francis' love for, openness to, and communion with God's creation as model for all Christians, recognizing that is both the gift of a benevolent Creator and a "book" by which we can know something of him. (10-12) He states his call thus:

The urgent challenge to protect our common home includes a concern to bring the whole human family together to seek a sustainable and integral development, for we know that things can change. The Creator does not abandon us; he never forsakes his loving plan or repents of having created us. Humanity still has the ability to work together in building our common home. ... I urgently appeal, then, for a new dialogue about how we are shaping the future of our planet. (13-14)

He then wastes little time in the problems he is calling to attention. It is somewhat regrettable that Laudato Si' is so often referred to as the "climate encyclical". As promised and hoped, Francis does address the matter of climate change head-on, coming down solidly on the side of the scientific consensus (23-26):

The climate is a common good, belonging to all and meant for all. At the global level, it is a complex system linked to many of the essential conditions for human life. A very solid scientific consensus indicates that we are presently witnessing a disturbing warming of the climatic system. In recent decades this warming has been accompanied by a constant rise in the sea level and, it would appear, by an increase of extreme weather events, even if a scientifically determinable cause cannot be assigned to each particular phenomenon. Humanity is called to recognize the need for changes of lifestyle, production and consumption, in order to combat this warming or at least the human causes which produce or aggravate it. It is true that there are other factors (such as volcanic activity, variations in the earth’s orbit and axis, the solar cycle), yet a number of scientific studies indicate that most global warming in recent decades is due to the great concentration of greenhouse gases (carbon dioxide, methane, nitrogen oxides and others) released mainly as a result of human activity. Concentrated in the atmosphere, these gases do not allow the warmth of the sun’s rays reflected by the earth to be dispersed in space. The problem is aggravated by a model of development based on the intensive use of fossil fuels, which is at the heart of the worldwide energy system. Another determining factor has been an increase in changed uses of the soil, principally deforestation for agricultural purposes. Warming has effects on the carbon cycle. It creates a vicious circle which aggravates the situation even more, affecting the availability of essential resources like drinking water, energy and agricultural production in warmer regions, and leading to the extinction of part of the planet’s biodiversity.... If present trends continue, this century may well witness extraordinary climate change and an unprecedented destruction of ecosystems, with serious consequences for all of us. A rise in the sea level, for example, can create extremely serious situations, if we consider that a quarter of the world’s population lives on the coast or nearby, and that the majority of our megacities are situated in coastal areas.

Is evident in this section, Francis is surprisingly literate in discussing the mechanics of this and other problems he highlights; it must be remembered (especially by politicians who seem to have forgotten) that the pope is himself a scientist, with a degree in chemistry. Just as strongly, he addresses the undeniable human consequences of climate change.

Climate change is a global problem with grave implications: environmental, social, economic, political and for the distribution of goods. It represents one of the principal challenges facing humanity in our day. Its worst impact will probably be felt by developing countries in coming decades. Many of the poor live in areas particularly affected by phenomena related to warming, and their means of subsistence are largely dependent on natural reserves and ecosystemic services such as agriculture, fishing and forestry. They have no other financial activities or resources which can enable them to adapt to climate change or to face natural disasters, and their access to social services and protection is very limited. For example, changes in climate, to which animals and plants cannot adapt, lead them to migrate; this in turn affects the livelihood of the poor, who are then forced to leave their homes, with great uncertainty for their future and that of their children. There has been a tragic rise in the number of migrants seeking to flee from the growing poverty caused by environmental degradation.

Yet the climate is just one of the many issues Francis calls us to respond to. He also discusses pollution (20), industrial waste (21), the western throwaway culture (22), water scarcity (28) and quality (29), and the loss of biodiversity (32-42). And after all this, he moves on to issues that are more sociological than ecological, echoing his conviction that humans are indivisibly connected with the rest of the creation (240): urbanization (44), societal breakdown (46), harmful effects of technology and media (47), and socioeconomic inequality (48-52). The scope of Francis' vision for human (or creational) flourishing, the depth of his compassion for humanity and nature, is breathtaking, as expressed in one of his concluding sentences:

it is no longer enough to speak only of the integrity of ecosystems. We have to dare to speak of the integrity of human life, of the need to promote and unify all the great values. Once we lose our humility, and become enthralled with the possibility of limitless mastery over everything, we inevitably end up harming society and the environment. (224)

In the face of all these problems, so often I turn away from most of them and focus on a few pet issues like climate change or recycling, if that. Francis' conviction shows me that this is due to the smallness of my heart; I simply can't bear to think in such length about the modern human condition, though I wish I could. Simply stopping manmade climate change is not nearly enough; this document reads like a blueprint for a truly Christian, truly human(e) way of being in the world. No one is fully equal to the task which he describes. This encyclical is not, I think, meant to be read by us as individuals, but as citizens, employees, members and supporters of movements and organizations that can tackle the big challenges, and, for some, as members of the body of Christ who are the real recipients of God's command to be stewards of his creation. To this end, in chapter two of the encyclical Francis compellingly lays out the Christian foundation for creation care, doing so much better than I did in my previous post on the climate.

Part of me is quite happy that Laudato Si' is getting as much publicity as it is, even if it arrives with much more fanfare than Ecumenical Patriarch Bartholomew's letter published years ago (in paragraphs 7-8 Francis favorably recognizes the prior contributions of Bartholomew, whose response to the present encyclical is also well worth reading, as is his joint response with the Archbishop of Canterbury). I hope that it will help to direct both public opinion and public policy towards courses of action that will bring about the kind of flourishing and harmony with the creation that he envisions. Yet it is hard not to finish reading it without feeling sobered at all the ways we harm ourselves and exploit the world around us, and what will be involved in shifting our present course.

Returning to the subject of the climate (maybe for the above reasons?), I appreciate how Francis is using his considerable moral authority to increase the pressure on climate change deniers. I could already tell you that it is immoral to reject humility, the basic facts, and public opinion in claiming without foundation that you know better about the climate than the overwhelming majority of climate scientists. But Francis also highlights our moral responsibility to live in harmony with (rather than selfishly exploit) the rest of the created world, and the human consequences of climate change, which will disproportionately fall on the poor and vulnerable who had a relatively small role in causing the rising sea levels, scorching droughts, or food chain collapses that made them into refugees. In other words, environmentalism is not just about self-preservation; it is about social justice and living as created beings worshipping our Creator. Climate change denial is not only blind (does anyone else appreciate the irony that religious leaders now seem to be more scientifically literate than a good deal of civil leaders?); it is callous for refusing to see and take responsibility for the consequences of our contributions to the problem at hand. As this excellent response from BioLogos says, Laudato Si' "makes a moral call for action based on the fundamental premises of the Christian faith – premises so fundamental that we can all, and must all, agree."

In summary: read Pope Francis' encyclical, or at least an executive summary of it. Recommend it to your friends and loved ones. The vision if offers, of a way through the ecological, technological, and sociological problems besetting modern-day humanity, is motivated by a compassionate heart that compels attention, if not partnership, not just from all Christians, but from all people. His seamless connection of this heart with the Christian faith and gospel is one of the best examples of evangelism I have seen in this day and age. For all the differences between my faith tradition and the pope's, I stand in complete agreement with him on the subject matter of this encyclical, and I hope that it finds traction in the hearts, minds, and lives of many.

Climate change: How we know it is real and what we can do about it

As the 2016 presidential election becomes harder to ignore, I realized to my surprise that so far I have been silent on an issue that is incredibly important to me and much more controversial than it should be. The time has come for me to firmly plant my flag concerning the reality of climate change.

The fact of the matter is that the Earth is warming at an unprecedented rate, most of this warming is due to human activity, it is already having an increasingly negative effect on biodiversity and our ability to thrive, and it will have catastrophic consequences if we do not take action soon to reduce our production of greenhouse gases.

The science

The scientific basis for global warming is well-understood, based on physical principles that are beyond questioning, and supported by observation. The greenhouse effect, the process by which atmospheric gases (primarily water vapor and carbon dioxide, but also methane and others) absorb and trap heat radiated by the earth, is entirely uncontroversial, supported by basic science and observation of the Earth as well as other worlds (especially Venus, where it is responsible for the lead-melting temperatures). Thus, as the concentrations of "greenhouse gases" in the atmosphere increases, we should expect them to retain more heat, producing a net atmospheric warming effect.

And this is exactly what we observe. Recent measurements show that the concentration of carbon dioxide in the atmosphere is steadily increasing. (The red line is the raw measurements, the black line is after correction for seasonal variation)

Over a somewhat longer timescale, we see that it might actually be exponentially increasing.

Lately, the growth rate of CO2 concentration has been about 2 ppm (parts per million) per year, or about 15 billion tons per year.

There is abundant evidence that this change in atmospheric carbon is anthropogenic (manmade). Human emissions of CO2 per year (see page 45 of that publication) are about 30 billion tons per year. This means that rather than producing a net emission of CO2, nature is in fact absorbing about half of the CO2 we emit. Additionally, atmospheric oxygen levels are steadily decreasing, which is just what we'd expect if the excess CO2 is being produced by burning carbon (i.e. fossil fuels) rather than by being released from a natural reservoir.

Over a longer timescale, this plot shows the correlation between the current rise in atmospheric carbon and human industrialization, beginning in the 19th century. By far the most obvious conclusion is that atmospheric carbon levels are increasing because we're putting it there by the burning of carbon-based energy sources.

One more plot shows the range of natural variation of atmospheric CO2 levels over a much longer timescale, and the relative magnitude and suddenness of the recent increase. Yes, carbon levels have changed in the past, but the present increase is virtually unprecedented in both its size and rapidness—150 years is the blink of an eye in geologic terms, and in that time we have already matched the increase in carbon over the past 11,000 years since the last ice age. Recently, atmospheric carbon reached 400 ppm—its highest level in the last three million years.

If the greenhouse effect works, this increase in atmospheric carbon should produce an increase in global temperatures. And it does. This plot shows five independent data sets of global surface or lower atmosphere temperature over the past 35 years. The second, smoother graph shows the data after removing the effects of the El Niño Southern Oscillation, solar variability, and volcanic emissions (several of the common natural explanations given for global warming). After filtering out these natural variables, a clear trend toward warmer temperatures remains.

This change in observed global temperatures can be correlated with a number of other variables, some of the most obvious of which are depicted below: receding glaciers and ice caps, rising sea levels and temperatures, changes in the migration and habitation of plant and animal species, and increasing humidity. Independently measuring and correlating all of these indicators considerably strengthens the case for a warming planet. And besides scientific measurements, the effects of global warming are already being felt around the world: increased flooding in coastal cities, record-breakingly hot months/summers/years/decades, and (in the past few years) the devastating drought in California. The effects of climate change are felt perhaps nowhere as strongly as in Pacific island nations like Tuvalu, the Marshall Islands, and the Maldives whose very existence is threatened by rising sea levels.

Again, this warming trend can be traced back to the previously mentioned manmade increase in atmospheric carbon levels by a variety of means. The independence with which these indicators can be measured and correlated with each other makes the case for anthropogenic climate change much stronger than it would be if it were based on only one variable.

The danger

You may be asking, "so what?" Carbon levels and global temperatures have fluctuated widely in the past (as previously mentioned, our current level of atmospheric carbon was last reached 3 million years ago), so how do we know that the era of global warming will actually be worse rather than just different? Well, as also previously mentioned, the difference between manmade climate change and natural climate change is one of both scale and rate. An optimistic estimate of 2° C of warming will push global surface temperatures to a level not seen since the last time we had this much carbon in the atmosphere, the Pliocene era three million years ago. And if we keep producing carbon at anything like our current rate, this number will likely be higher. Most species alive today didn't even exist tens of millions of years ago when things were last this hot, so we can't expect them to be able to adapt.

Even more significant is the fact that while climate changes naturally over the course of thousands or tens of thousands of years (during which greenhouse gas emission and absorption remain roughly balanced at all times), manmade climate change is operative over just a few hundred years—orders of magnitude faster than the natural rate. Past instances in which atmospheric carbon levels and global temperatures changed suddenly and in an imbalanced way (as they are doing today), due to large igneous provinces or other causes, almost always resulted in mass extinction events—and it is very likely that our actions are sending the Earth into another one, as they are producing the same symptoms by the same means. The stress we have placed on species and ecosystems through other means like pollution, habitat loss, overhunting/fishing, and the introduction of invasive species makes it even harder for them to adapt to manmade climate change as they have to natural climate shifts in the past. This article explains these difficulties in more depth.

While warming temperatures may bring some positive effects, like improved agriculture and vegetation activity at higher latitudes and an ice-free Northwest Passage, the negative effects are expected to be far greater. These include unhappy things like decreased water supply and desertification (as in California), increased danger of heat stress, the growth of oxygen-poor zones in the ocean, extinction of numerous vulnerable species and the loss of biodiversity, and the displacement of hundreds of millions due to sea level rise. All of these things will carry catastrophic economic consequences for developing and developed nations alike. Still more troubling are effects like decline in global phytoplankton and the leakage of methane from formerly frozen areas that will create positive feedback, further intensifying the warming of our planet. In theory, if the planet warms enough to push the water vapor concentration in the atmosphere to a sufficient level, the feedback could become a self-sustaining loop that would turn the Earth into a second Venus (though we would likely already be doomed well before it got to this point).

The consensus

The scientific consensus on climate change is clear and unequivocal. A survey of peer-reviewed climate science papers found that 97% of the papers expressing a position explicitly affirm that anthropogenic climate change is real. If this figure seems surprisingly low, keep in mind that the 3% includes implicit (rather than explicit) endorsements, implicit rejections, and no opinions. Another, similar survey which only counted explicit rejections of anthropogenic climate change found that 24 out of 13,950 articles reject global warming—just 0.17%. This consensus is even stronger (at least 98% explicitly affirming) in more recent papers.

In light of all this, it saddens me to see so many of our nation's leaders (and the people who voted for them) willfully ignore the scientific consensus in favor of their own fantasies about climate change: that it is not happening, that is it is not a problem, that it is not caused by us, that there is no consensus, or that there is no need for them to take action because "I'm not a scientist" (and, apparently, not willing to trust them either). Certainly the media, in its well-intentioned dedication to balance, is partly responsible for enabling this ignorance: it creates the illusion that climate change is a two-sided issue under discussion rather than a matter of scientific fact. But really there is no "debate" or "conversation" regarding the reality of climate change; there is only an overwhelming consensus and those who (all too often for political or ideological reasons) refuse to accept it.

As an analogy, consider the fact that due to tidal acceleration, the Moon is moving away from the Earth at a rate of about 3.8 cm/year. This trend is not immediately or intuitively obvious to an observer, but it is well explained by basic physical principles and verifiable by multiple methods: studying ancient records of eclipses to establish the Moon's position in the past, gravitational data from satellite laser ranging, and simply bouncing light pulses off the retroreflectors left by the Apollo astronauts and measuring the return delay. Scientists are just as certain that anthropogenic climate change is happening as they are that the Moon is drifting away from the Earth. I have never heard anyone express doubt about the latter. Why is the former any different—because of its implications for how we live? Our own desires, interests, and preferences cannot change the truth of what we are doing to the climate.

The theology

My knowledge of the fragility and beauty of the Earth and our dependence on it, as well as my own experiences in nature, would be sufficient to instill in me a deep and abiding concern for environmental issues, especially anthropogenic global warming, dangerous as it is. But as a Christian, I have another, even stronger foundation for environmental concern and action.

In Genesis 1 God creates the heavens and the Earth (v. 1) and all the life on the Earth, declaring everything that he had made "very good" (v. 31). He also creates mankind in his image, to fill the Earth and subdue it and have dominion over nature. (v. 28) Does this mandate give us license to do as we please with the environment? No, for it must be considered along with the innate goodness of created nature and our role as God-appointed regents over it. If the creation is really good, and not "fallen"/evil or simply morally neutral raw material for our own designs, then by harming it we are harming God's handiwork. The image of God in man is not the only reason for human worth and dignity; simply being created at all conveys great worth and value. The mandate uses militaristic language ("subdue", "have dominion over") because of the present, frustrated state of the creation (cf. Rom 8:19-23), but this dominion always has as its intent wise, beneficent rule and redemption as God himself works, never exploitation or destruction.

The Psalms contain abundant examples of the value of creation as it reveals the glory of God. In Psalm 19 "the heavens are telling the glory of God" to the ends of the earth and the sun "like a strong man runs its course with joy". Psalm 33 praises God (through the Psalmist's ancient understanding of the cosmos) as the creator and ruler of the heavens, the earth, and the sea. Psalm 104 goes into considerably more detail, poetically describing the act of creation as well as God's ongoing governance of the created order, providing food for man and the animals; even the cycle of life and death is the occasion for praise. Psalms like these express what I have heard described as a sacramental view of nature which Fr. Stephen Freeman describes as the opposite of modern secularism, the reckoning of all the workings of the cosmos as a ceaseless act and a voiceless hymn of worship to their maker.

As an Orthodox Christian-to-be, I am happy to be part of a church which faithfully preserves and teaches this understanding of the cosmos. It is truly the basis for robust, authentic Christian environmentalism. As proof of this, one need look no further than the current ecumenical patriarch, Bartholomew. Like Pope Francis, he is deeply concerned about the human impact on the environment; unlike Pope Francis, he has already published a strongly-worded and very wise encyclical which expresses a theological basis for caring for the creation much better than I can (and takes a strong stance on climate change, much like the one the Vatican is expected to take). Even if you haven't been reading all the links I've been posting thus far, take just a few minutes and read it

One other way Christian teaching can contribute to the conversation on climate change is in its abiding concern for the poor. It is an unhappy fact of global warming that the nations most affected by it tend to be poor and developing (as well as very low in carbon emissions), while the nations least affected are predominately the wealthy nations responsible for causing it in the first place. It is a textbook negative externality on a global scale, a terrible injustice. Prominent among the Christian's reasons for environmental concern should be the awareness of the possible unjust effects of his/her actions on the poor who stand to lose the most to climate change—their crops, their livelihoods, even their homes and their lives.

In light of all this, arguments fielded by Christians in opposition to environmentalism are revealed for the falsehoods they are. Since they seem to exist solely among laypeople and not among scientists or theologians, I will not attempt to state them in a clearer, better-supported form as I usually do. These are not carefully-considered theological responses with any kind of historical pedigree or arrived at after careful reflection; they are from-the-hip answers that use Christian-esque ideas to justify a false position arrived at due to other factors.

First, I have heard it argued that God, as creator, is sovereign over nature, and that man doesn't have the power to change it or thwart his plans. My first response is that this is simply factually false. Man evidently does have the power to cause global-scale environmental changes because we are doing so and have already done so. This is simply undeniable, supported by reliable, repeatable observations; for instance, as shown above, we have demonstrably increased the carbon concentration of the atmosphere by about a third. Theological arguments can't falsify a scientific theory; only a scientific argument can. As Mark Noll explains in relation to young-Earth creationism in his book The Scandal of the Evangelical Mind, authentic Christian thinking requires listening to both "books" of God's revelation: Scripture and creation, not using your interpretation of one to contradict what we can know through the other. To do so is, ironically, to deny God as creator in order to confess him as sustainer of the creation.

Further, we know that God created us in his image as free, responsible beings with real moral agency and the ability to make real moral choices. This is implicit in all of the Bible's ethical commands, which wouldn't make sense otherwise, and has always been the teaching of the Orthodox Church. Sidestepping discussions of the exact nature or extent of this freedom, God's sovereignty obviously doesn't mean that he defends the integrity of his image in man by intervening to stop us from wronging or killing each other. Why then should we expect him to prevent us from sinning against the environment? There is no biblical support for such an idea, and plenty for the kind of Christian environmental ethic I sought to lay out above.

Additionally, this argument sidesteps the question of whether and how Christians are to care for the environment; it simply claims (without serious justification) that God will somehow restrain or prevent the negative consequences of our failing to do so, so there is no need to try. But if we really are appointed as stewards and even priests of the rest of the creation, then this argument is saying in effect that we should simply ignore this vocation because there was really no reason for God to give it to us in the first place. This is horribly irresponsible and dualistic, not to mention hubristic. "But who are you, O man, to talk back to God?" (Rom 9:20) By contrast, it is not hubristic at all to believe, on the basis of multiple independently measurable indicators, the sobering truth that human activity is having a major effect on the Earth's climate, which we have a mandate to care for. Rather, it is the beginning of humility and repentance.

The other argument I sometimes hear is similar to the first, but even worse. It is the sentiment that because Jesus is coming back to bring the old creation to an end and inaugurate the new, we don't have to be especially concerned about the environment. Similar to the previous argument, it basically states that we don't need to care about the effects of human activity on the environment because God will intervene to prevent them, in this case by returning to bring about the end of the world. In other words, it presumes that Jesus will return before climate change can begin to have catastrophic effects on future generations. But, in Jesus' own words, "watch therefore, for you know neither the day nor the hour." (Mat 25:13) Jesus was clear about few things relating to his return, but he was crystal clear about the fact that we can't know when it will be. (See also Mat 24:36,44,50; Mar 13:32; Luk 12:40,46; Acts 1:7) Like the first argument, it sidesteps any kind of teleological discussion of our appointed role as stewards of the creation, focusing only on why we will supposedly be spared from the consequences of scorning our calling.

Why not justify other corporate sins in this way? Why not support slavery, since Jesus will come back to break every chain? Why not selfishly exacerbate the suffering and poverty of people in developing countries (which, incidentally, is one of the effects of global warming), since Jesus will return to wipe every tear from their eyes? "And why not do evil that good may come?" (Rom 3:8) The return of Jesus and the last judgment, far from a cosmic reset button undoing our sins, will be a day of reckoning in which we will be called to account for all that we have done (Mat 25:31-46, Rom 2:6-8, 14:12, 2 Tim 4:1, 1 Pe 4:5, Rev 20:12). It is hard to imagine a greater folly than expecting the day in which everyone will be judged for what he has done to be the occasion for our escape from accountability for sins against the environment.

Edit: The sovereignty of God, invoked in the first counterargument, is relevant to discussions of the climate in another way. The Christian faith involves an unstoppable hope, based on the Incarnation, crucifixion, and resurrection of our Lord, that is sufficient to overcome even the grim certainty of death. Paul, describing this hope, says powerfully, "I am sure that neither death, nor life, nor angels, nor principalities, nor things present, nor things to come, nor powers, nor height, nor depth, nor anything else in all creation, will be able to separate us from the love of God in Christ Jesus our Lord." (Rom 8:38-39) So one implication of the sovereignty of God is that we are to remain hopeful and not despair no matter how bad things seem, since for many Christians they have seemed much worse. But not to fear is not to do nothing. Like any other issue incumbent on the Church, climate change demands a response, but that response should be out of hope, not fear or gloom.

What can we do?

In the face of these terrifying visions, and the continued politicized denial of climate change, especially by Republican leaders, it is very tempting (certainly for me) to simply despair of hope that anything can be done. At times like this it's very beneficial to rest and remind myself of some of the reasons for hope that we can actually address the climate crisis. But if you grasp the magnitude of the problem and the need for broad and deep action to address it, then remaining a bystander stops looking like a suitable option. I will try to present ways I have found to take personal action against climate change. Most of them are not that hard!

First, you can reduce your carbon footprint. Your carbon footprint is the sum of the carbon emissions caused by your actions and lifestyle, both directly (i.e. by driving or burning other fuels) and indirectly (e.g. by buying or using products that require carbon to produce or transport). Some ways to do this include:

• Use less heating and air conditioning in your home. If you are a homeowner, this might mean insulting your home better to avoid having to heat it as much or installing a "smart" thermostat that only regulates your home's temperature when people need it. If, like me, you rent an apartment, you can still leave your thermostat at a lower temperature in winter and rely more on fans and opening/shading windows than air conditioning in the summer.
• Minimize your energy usage. Ways to do this include using compact fluorescent bulbs for lighting (or, better yet, long-lasting and super-efficient LED bulbs), turning off lights when you leave a room, turning your computer off when not using it, and plugging devices that use power even when turned off (e.g. lots of electronics) into a power strip so you can fully de-power them when not using them. As previously mentioned, minimizing your use of heating and air conditioning also helps with this. If you are a homeowner, you can also try to install energy-efficient (e.g. Energy Star) appliances.
• Use less hot water; heating water takes a lot of energy. If possible, you can do this by installing more efficient shower heads/faucets/toilets. Homeowners can also turn their hot water temperature down and/or ensure that their water heater is well-insulated.
• The classic trifecta: reduce, reuse, recycle. This boils down to consuming and throwing away as little as possible. If you're unsure about what you can recycle, your city's web site should tell you. (Here is the one for Minneapolis as an example)
• Drive less or not at all. When possible, use alternate forms of transportation like walking, cycling, carpooling, or public transportation. This may not be easy, but besides the environmental benefits it will also save you money, especially if you are able to completely replace owning a car with other ways of getting around. I am almost through my third post-college year without a car and loving it. I spend $85 a month on my bus pass and a total of about $200 a year on parts and maintenance for my bike. Not only do I save a lot of money, I love not having to spend lots of time driving or (as is all too often the case) sitting in traffic. Once we are married, my fiancee Marissa and I plan to own one car between us, which should be more than sufficient for our needs. This option may require some bigger lifestyle modifications, but can be quite worth it and have a major impact on your carbon footprint.
• Eat less meat, especially red meat. Producing a given amount of calories of meat uses a lot more resources than producing the same amount of calories of plants. Even if you don't go fully vegetarian, reducing the amount of meat in your diet can make a sizable difference. Apparently minimizing your consumption of rice is also beneficial, since most rice is grown in methane-emitting paddies. Eating locally-grown food is also an obvious step (reducing fuel costs of transporting it), as is avoiding wasting food.

Second, you can offset your carbon footprint. This means supporting environmental projects that remove an amount of carbon from the atmosphere equal to the amount you put in. The cost of this is apparently just $15 per metric ton. The average carbon footprint of an American is 27 tons per year, which translates to an offset of $405, or just $33.75 per month. This is a surprisingly low price to pay to become "carbon neutral", and of course you can decrease it by lowering your footprint. This handy site lets you estimate your carbon footprint and donate to offset it.

And third, you can take action beyond your individual/household's carbon footprint. You can support organizations that are helping to fight climate change and promote the welfare of the environment like The Nature Conservancy, the Environmental Defense Fund, or the World Resources Institute. (The very useful website Charity Navigator can help you find another organization to support if you like) Or you can join the public conversation addressing climate change by signing petitions, writing to your elected officials about your concerns, or simply by telling others about it to raise awareness, perhaps by sharing concise, persuasive resources on the web (hint hint). The strategy and tactics of dealing with global warming are much more complex subjects than the basic scientific facts. Once we are in agreement that anthropogenic climate change is real, there is plenty of room for diversity of opinion on what to do about it, how to balance short-term needs and economic realities with the long-term need not to cook the planet to death. My goal in shutting down climate change denial is not to end constructive conversation, but to make it possible and invite more people into it by showing the obscurantist, anti-science rhetoric of denial for what it is and calling us to rise above it. If we are to resolve the climate crisis, we need all the voices—and hands—we can get.