According to Wikipedia, "Viktor Frankl in his book Man's Search for Meaning, recommended "that the Statue of Liberty on the East Coast should be supplemented by a Statue of Responsibility on the West Coast." Apparently, a group has already designed such a Statue of Responsibility, and is in the process of raising funds to build it.
Above: Drawing of the proposed Statue of Responsibility
What if, instead of a single statue, the US were to construct a series of monuments that, to show our commitment to responsibility, also sequestered CO2 from the atmosphere?
This is more or less what a team of Dutch scientists have proposed with their "olivine hills" concept. The goal of the project would be to mine tens of thousands of tons of olivine, a silicate rock that binds with CO2 when it is exposed to water, and construct a series of hills out of this material. Then, when rain falls on these hills, CO2 would bind to the olivine, sequestering it from returning to the atmosphere for tens of thousands of years.
Unfortunately, this proposal would be expensive and wouldn't sequester all that much CO2: assuming each hill uses 25,000 tons of olivine (the Great Pyramid of Giza used 5.5 million tons of limestone in comparison...) and we built one hill for every 100,000 people in the US, we would end up sequestering some 100 million tonnes of CO2 (only 2% or so of total US emissions). At a cost of $50/ton of olivine, we would end up spending $4B on olivine alone -- if labor and other costs represented an equal sum, the monuments would remove carbon at a price of about $80/ton -- nearly 8 times higher than current carbon prices in California's cap and trade scheme.
Nevertheless, it would be really cool. We could even plant trees, install solar panels, grow produce, build parks, and/or build more traditional monuments on top of such olivine hills to maximize their symbolic and actual responsibility. And these monuments would create lots of jobs and potential tourist revenues as an added bonus.