what was the change in ground leases between 2012 and 2013 in millions?
56 / 57 management 2019s discussion and analysis of financial condition and results of operations junior subordinate deferrable interest debentures in june 2005 , we issued $ 100.0 a0million of trust preferred securities , which are reflected on the balance sheet as junior subordinate deferrable interest debentures . the proceeds were used to repay our revolving credit facility . the $ 100.0 a0million of junior subordi- nate deferrable interest debentures have a 30-year term ending july 2035 . they bear interest at a fixed rate of 5.61% ( 5.61 % ) for the first 10 years ending july 2015 . thereafter , the rate will float at three month libor plus 1.25% ( 1.25 % ) . the securities are redeemable at par . restrictive covenants the terms of the 2011 revolving credit facility and certain of our senior unsecured notes include certain restrictions and covenants which may limit , among other things , our ability to pay dividends ( as discussed below ) , make certain types of investments , incur additional indebtedness , incur liens and enter into negative pledge agreements and the disposition of assets , and which require compliance with financial ratios including our minimum tangible net worth , a maximum ratio of total indebtedness to total asset value , a minimum ratio of ebitda to fixed charges and a maximum ratio of unsecured indebtedness to unencumbered asset value . the dividend restriction referred to above provides that we will not during any time when we are in default , make distributions with respect to common stock or other equity interests , except to enable us to continue to qualify as a reit for federal income tax purposes . as of december a031 , 2011 and 2010 , we were in compli- ance with all such covenants . market rate risk we are exposed to changes in interest rates primarily from our floating rate borrowing arrangements . we use interest rate deriv- ative instruments to manage exposure to interest rate changes . a a0hypothetical 100 a0basis point increase in interest rates along the entire interest rate curve for 2011 and 2010 , would increase our annual interest cost by approximately $ 12.3 a0million and $ 11.0 a0mil- lion and would increase our share of joint venture annual interest cost by approximately $ 4.8 a0million and $ 6.7 a0million , respectively . we recognize all derivatives on the balance sheet at fair value . derivatives that are not hedges must be adjusted to fair value through income . if a derivative is a hedge , depending on the nature of the hedge , changes in the fair value of the derivative will either be offset against the change in fair value of the hedged asset , liability , or firm commitment through earnings , or recognized in other comprehensive income until the hedged item is recognized in earnings . the ineffective portion of a derivative 2019s change in fair value is recognized immediately in earnings . approximately $ 4.8 a0billion of our long- term debt bore interest a0at fixed rates , and therefore the fair value of these instru- ments is affected by changes in the market interest rates . the interest rate on our variable rate debt and joint venture debt as of december a031 , 2011 ranged from libor plus 150 a0basis points to libor plus 350 a0basis points . contractual obligations combined aggregate principal maturities of mortgages and other loans payable , our 2011 revolving credit facility , senior unsecured notes ( net of discount ) , trust preferred securities , our share of joint venture debt , including as- of-right extension options , estimated interest expense ( based on weighted average interest rates for the quarter ) , and our obligations under our capital lease and ground leases , as of december a031 , 2011 are as follows ( in thousands ) : .

|  | 2012 | 2013 | 2014 | 2015 | 2016 | Thereafter | Total |
| :--- | :--- | :--- | :--- | :--- | :--- | :--- | :--- |
| Property Mortgages | $52,443 | $568,649 | $647,776 | $270,382 | $556,400 | $2,278,190 | $4,373,840 |
| Revolving Credit Facility | — | — | — | — | 350,000 | — | 350,000 |
| Trust Preferred Securities | — | — | — | — | — | 100,000 | 100,000 |
| Senior Unsecured Notes | 119,423 | — | 98,578 | 657 | 274,804 | 777,194 | 1,270,656 |
| Capital lease | 1,555 | 1,555 | 1,555 | 1,592 | 1,707 | 42,351 | 50,315 |
| Ground leases | 33,429 | 33,429 | 33,429 | 33,429 | 33,533 | 615,450 | 782,699 |
| Estimated interest expense | 312,672 | 309,280 | 269,286 | 244,709 | 212,328 | 470,359 | 1,818,634 |
| Joint venture debt | 176,457 | 93,683 | 123,983 | 102,476 | 527,814 | 800,102 | 1,824,515 |
| Total | $695,979 | $1,006,596 | $1,174,607 | $653,245 | $1,956,586 | $5,083,646 | $10,570,659 |

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ground_leases_2012_2013 = 33429
ground_leases_total = 33429
percent_change = (ground_leases_2012_2013 - ground_leases_total) / ground_leases_total
answer = percent_change